Sewage Maceration Is As Gross As It Sounds

Day to day, few of us really contemplate what’s happening on a deep, mechanical level when we use the toilet. The business is done, the toilet is flushed, and we go about our day. However, the magnificent technology of indoor sanitation should not be sniffed at, given the manner in which it facilitates a cleaner, more comfortable existence for us all.

The vast majority of flush toilets rely on the benefit of gravity to remove waste from the house. This necessitates that the toilet be installed above the sewage lines that exit the house. For most installations at ground floor and above, this isn’t a problem. However, on occasions you may encounter basements or houses with rooms at lower levels where a regular toilet simply won’t work. Obviously, a pump is in order, but human sewage being a mixture of liquids and solids makes this impractical. Instead, it must be turned into a slurry that can be pumped; a process known as sewage maceration. Buckle up!

How It Works

A typical macerator unit installed behind a toilet. This unit is installed behind a wall, though many installs simply elect to leave the unit directly behind the cistern.

A macerator is, at its heart, essentially a blender for sewage, combined with a pump. They’re commonly used in the home when its desired to install a toilet at a level beneath the main sewer line, or to do so without drilling through the floor. Thanks to the pump, they don’t need to rely on gravity and can be used to move sewage tens of feet vertically and hundreds of feet horizontally.

Perhaps the most representative model of macerator for the home market is the Saniflo, which uses a mains-powered motor to spin a steel blade to chop the sewage into a slurry, before pumping it using a typical impeller design. These are often combined with special toilets with rear outlets that are otherwise uncommon in the US market, and can also be plumbed to use the pump with sinks and showers as well. Upon water and waste entering the toilet, a pressure switch is triggered that turns on the system, breaking up the matter with the blades and pumping it away. The limitation of this design is that the maceration blades can become jammed, particularly with fibrous material such as wipes or sanitary products. This can lead to results that are only humorous if they’re happening to someone else, as repairing a jammed system typically involves dismantling the unit and the sewer line, which is typically full of the horrible waste you were trying to get rid of and doesn’t typically have an on/off valve. Higher end models exist, which pack heavy duty “grinding” blades to break down such material, but no system is perfect and jams are still common.

Sewage macerators used at temporary accommodation at a mine site. They’re necessary whenever sewage needs to be pumped – even if height isn’t an issue, horizontal distance may be.

The real issue with sewage maceration is not that it works, but that it sometimes breaks down, and when it does, it’s a filthy mess. A system of motors, pressure switches, and valves will always be less reliable than a simple hole in the floor, and more prone to failure. With the bonus of being installed below the sewer line, any maintenance will typically lead to a spill of raw sewage. It’s a peril this writer hasn’t experienced in 30 years of typical gravity toilet use; one must suspect few home maceration systems are quite so reliable. Regardless, it should lead any homeowner to think carefully about whether having a toilet in the basement is quite worth the complications.

Industrial Maceration

Industrial-grade machines like these are installed throughout municipal sewage systems to break up those things you really weren’t supposed to flush. Like goldfish.

Of course, maceration isn’t just for the home gamer. Larger systems are used at the municipal level to break up waste and pump it through treatment facilities. This has become a more important issue in recent years, as more ignorant citizens flush wipes and other matter that doesn’t break up in water. Rather than attempt to educate the populace, many cities have simply elected to solve the issue with heavy machinery. Some manufacturers are even marketing heavy duty grinders to do the job. If the trend continues, it should be possible to flush a Hot Wheels by 2037 without undue repercussions from the local authorities.

While already familiar to the plumbing fraternity, we hope this article has served as an education in the how and why of pumping sewage. It can be done, and at relatively low cost — albeit with significant consequences when it goes wrong. May this aid your decision making process when it comes time to remodel your poolhouse, or when your significant other asks if the downstairs bedroom should have an ensuite. Good luck, and happy plumbing!

100 thoughts on “Sewage Maceration Is As Gross As It Sounds

  1. >[Industrial maceration] has become a more important issue in recent years, as more ignorant citizens flush wipes and other matter that doesn’t break up in water.

    I don’t think it’s always that. In my region of the UK a lot of storm drains are linked to the sewage network, and so anything lying in those drains is liable to get dragged in too. It’s still a people problem, just much more dispersed.

    At any rate, you’d be surprised what people flush for whatever crazy reason. There was an incident of flushed underwear contributing to a pipe bursting and the road which ran over it collapsing in 2007 in England:

      1. Mike, you recall the Milwaukee sewer problem of a few years back?
        They had a combined storm/sewer system, and when rain (or spring melt-off) overloaded the system,
        raw sewage was dumped in Lake Michigan, and later taken in by the municipal water supply.
        A child died as a result of the diseased water.

        1. Pacifica, a small city near San Francisco, had a similar problem a few years back. Heavy rain fall over whelmed the sewer processing capacity and untreated sewage had to be pumped into the ocean. Residence of Pacifica are still paying off a ~$20million fine from that incident.

          The ‘long term’ solution (or hack) is to build a giant sewage buffer/holding tank to allow holding some amount of raw sewage until the sewage surge is over there is sufficient processing capacity to start processing the contents of the holding tank. After the tank is emptied, it has to be disinfected…

          There is no interest at the city/county/state level for addressing either the limited sewage processing capacity, nor separating storm water handling from sewage handling.

          1. Seems to me that the long term solution would be to separate the storm water from sewage.

            Here in the Phoenix area, our soil is heavily compacted and not very permeable. We have long spells with no rain, and very short bursts of massive amount of rainfall (monsoon season). There are drainage canals and retention basins (usually city parks) everywhere. At least once or twice every year, we’ll get a downpour and our parks will fill up with a few feet of water. Drywells are sunk across the park to allow the water to drain back into the groundwater.

            The system does get overwhelmed from time to time, leading people to drive through flooded underpasses every couple of years. But it seems to work pretty well overall. Growing up in the Bay Area, CA, I recall storm drains usually imprinted with “Don’t dump into storm drain. Empties to the sea.” or something similar. It’s been a couple of decades since I’ve lived there though…

          2. I don’t know about regulations in the states, but in South Africa it’s illegal to discharge stormwater into the sewage system. Obviously some water may ingress into the system and some people have no regard for the law, so the sewage plants are designed for at least twice the base flow (the smaller the plant, the larger the factor) to allow for the surge during storms.

            We also have huge “maturation ponds”, as they call it, on these plants for longer term storage should the plant malfunction for some reason…

            What you suggested is the norm over here. Maybe Pacifica outgrew it’s treatment system faster than expected, or it was a freak accident, or the plant was under designed. I worked on a few projects where politics and nonsense always stand in the way of service provision, though.

        2. It’s not uncommon for older municipalities to have systems that handled both in one system. A lot of the older cities in the NE United States are plumbed this way.

          It’s also not uncommon for these systems to overflow during the spring melt or during heavy rainfall. They were all designed to overflow once their intake capacity is exceeded and most of the time when this happens the raw sewage is diluted with so much storm water and ice melt runoff that the sewage is a small fraction of what’s being dumped. Now these large cities are putting in huge underground buffers to contain the excess runoff so it can be processed later.

          The outbreak that caused over 400,000 people to get sick in the Milwaukee area in 1993 was caused by Cryptosporidium and Giardia. Although this was caused by the sewage overflow the sewage itself did not cause the outbreak. The cause was high concentrations of Cryptosporidium and Giardia protozoan pathogens that were suspended in the water caused by the overflow. These don’t come from raw sewage. They come from streams, rivers and groundwater that gets passed through when the system overflows. And once these pathogens settled out of the water into the lakebed the outbreak disappeared.

          Milwaukee still has a combined storm/sewer system. And they still average over 2 overflow events a year. And when the perfect set of events occur again, where suspended (non-sewage) solids from their outflow gets sucked back into their water system, Milwaukee will have another Cryptosporidium and Giardia outbreak.

    1. Every year I flush 15L of used engine oil down the drain when I change oil in my three cars. I know it’s not very ecological but there’s no other way to dispose it without paying (thanks EU for your regulations!)

        1. My local tip has a used oil disposal tank. No charge to use it.
          So I don’t think that you can blame EU regs. (It has been there for decades, it didn’t just appear magically after Brexit)

      1. Years ago when I was kid in NY State my dad built a used engine oil fired stove for the garage.

        He used a 55 gallon drum and a oil drip feed from a tank we mounted outside. We would start a fire with scrap wood and then turn on the drip feed. The oil would drip onto the burning wood. It worked very well and smoked very little once the stove warmed up.

      2. If you know it’s not very ecological then pay for it! Blaming EU regulations is ridiculous – most countries have similar requirements because it’s a hazardous product that needs special disposal to avoid poisoning our surface and ground waters. Tipping it down the drain is just unscrupulous.

        1. Of course it is not acceptable to flush the oil down the toilet. But EU con not be blamed for THIS problem. Here in Vienna (Austria, also EU) you can dispose of used oil for free at waste collection centers from the city. They take even used cooking oil for recycling (probably biodiesel), but of course not mixed.
          And it is necessary, that they take it for free, because naturally, if they took money for it, most people would just flush it.

      3. Wait… You own three cars and change the oil every year (I don’t know anyone that does that) but you are too cheap to dispose of it properly? I dislike the EU as much as the next guy, but you’re the problem here. If it’s such an issue, why not put it in a container and leave it at city hall? If you’re dumping your waste on society, at least do it in the least impact-full way.

      4. In most (if not all) EU countries petrol stations will take it FOR FREE. There are even companies that will buy it from you. For your amusement: every litre of used engine oil can turn million litres of clean water into waste. Good job.

      5. Your comment could be troll, or, not, no way of knowing. This comment represents the twos of humanity.. Screw over your neighbor, if it saves, yourself some coin. Here in the US, most ser auto servicing location, accept used oil, because they sell it to te recylelers. Here in the use, our water bills, contain, fees for maintaining the saniray swer system, trash disposa

      6. To be blunt, doing it is bad enough but then admitting it and telling the world you’re a tight wad who doesn’t give a sh1t about anything says rather a lot about you. Guess it’s not by chance you don’t post using a name… #GodHelpUs

      7. Actually, it’s not the EU regulation with makes you pay but the regulation of the member state you live in.

        In Germany, the regulation is that shops which sell you oil are required to accept you waste oil, free of charge (they might ask for your receipt).

        If the shop is fussy (or you did not buy the oil but stole it, so you got no receipt), simply put your waste oil into the oil canisters and place them at the doorstep of the shop. Preferably at night. Corona bonus: you can onw wear a face mask without raising suspicion.

      8. I hope “they” get you at some point. You know what that amount of oil does to the environment???
        Damn I don’t say that often but I HATE you for that. Pullig the EU out of your hat as an excuse is just pure disgusting.

        Don’t know where you are but I hope the authorities catch you and put a hefty fine on you… Damn…

        1. Oil damages the environment in two ways. When it creates a film over water that interrupts the oxygen exchange between air and water. And when it coats animals – like in the Valdez disaster. But when mixed with the environment oil decomposes just like any other hydrocarbon.

          We used to dump waste oil along the fence line years ago. Most everyone else who changed their own oil did too. It made great fence line weed control. But you had to keep dumping or the weeds and grass would come back in two years. Why? Because the used oil would decompose!

          1. It couldnt be that it would wash away. Its not like oil floats on water. Inconceivable!

            O wait yea it washed away to a place where animals congregate to get water and fish breed. The term is light non aqueous phase liquid, which is easier to remove than the dense variety, but that in no way means less destructive. Especially when you consider how something might decompose. It always comes down to bacteria. Well there are not oil eating bacteria just waiting in our fields to gobble up any we might dump over our fence. Eventually, at the site of a large spill, and im talking exxon size, you will get bacteria after years that will eat it slowly if it is concentrated and immobile in one place. Like the place we got it from. But when it can just wash around with the water it does not decompose. It only dilutes. Meaning that oil you would pour out is likely still out there wreaking havoc but on a much smaller scale over a MUCH wider area. So if you see a crippled duck around your home just think, that was me!

      9. I’d look around more for someone or a site that can burn the oil. No waste oil burners or diesel drivers that can re-use for fuel in the EU? Hunt around so not being dumped in the drain… that’s like sort of free energy.

    2. In some places, not only are the storm drains NOT connected to sewage – but there’s also effort to reduce what’s in the sewage line.

      “grey water” takes runoff from laundry, shower, kitchen sink etc. and removes solid waste (eg. food scraps). The remaining water can then be used on gardens, reducing the water bill and easing the stress of drought conditions.

  2. I am glad that I don’t have to service or repair those- what a crappy job. :)

    In all seriousness, though- this is actually a cool article about the things people don’t like to deal with.

    I personally don’t do anything more than minor plumbing repairs to my ~50+ year old house- usually what happens is something _else_ breaks in the process and I end up having to call a plumber anyway, and/or make multiple trips to the hardware store to get the additional parts. lately, I just save myself the stress and hassle and call the plumber- they _usually_ have everything they’ll need on the truck to fix the collateral damage.

  3. It sounds gross, and ok – is… but with an extra set of valves at the installation one easily isolates the pump. This is the installers duty to design in. A good catchpan under the couplings and the smelly mess is a couple gallons. Odds are, you’ll not be like me and you’ll hire it out anyway. Just leave working space during the install and adequate cleanouts. Make CERTAIN your designer-installer is TOLD to pre-think all this out and not scrimp to be the low bidder. Each item will add 10-20$ parts and possible equal in labor. Your biggest enemy is wham-bam, done and gone guys. Otherwise it’s an expensive circuit without a safety fuse in a box with tamper-resistant screws. Some mobile homes have these mascerators. Really, it’s no biggee if the install is good. Rubber gloves, safey glasses or face shield is a plus. With a box fan to dilute the smelly air, you’re golden.

  4. In my job doing commercial building maintenance, we had one facility with one of these horrible devices. Fortunately, that facility was a home for clergy, so it was easy convincing that that the cellar sink and toilet was for liquids only. In the 5 years or so I worked on that building, I never had to touch the dreaded sewage pump (and I probably would have called in Roto-Rooter to do it anyway, as I didn’t get paid enough to deal with that!).

  5. I’ve been using a homebuilt macerator to empty my RV tanks for a few years now. I made it out of a garbage disposal, RV drain hose and 50 feet of pool drain hose. It chews and pumps the poo stew over to my sewer cleanout surprisingly well.

    There are commercial versions available, but they cost around $400 (I built mine for around $80).

    1. The 12v/30A version is about $70 US if your batteries are nearby, which ours are.
      This empties our black tank through a 25ft 1″ hose at 3′ lift in about 5 minutes. This is right about at the limit though as the thermal shutoff for that pump triggers at about 7 minutes.
      Combined this with esphome, two linear actuators for the dump valves, a couple sprinkler valves, and a foil capacitive sensor for level.
      Automated *locally* on a single ESP32 so loss of network doesn’t interrupt the sequencing. Important.

      Just make sure the automation doesn’t trigger while moving. :)
      I have yet to implement a lockout, but the results of forgetting seem to be dire enough thus far.

          1. I live in Arizona. What’s rust? Haha.

            Good guess though. I’ve daily-driven mustangs for the last 30 years or so. And my name is Russ.
            Please forgive me, It was the most clever username my 19 year old brain could come up with at the time. :)

      1. That would be a cool setup for PET I’d think, drop clean PET in, drops into a hopper fed hot end, and you have a mechanical turntable arrangement, or a cooling drum and winder, that just lets you “print filament” in much the same way that programmable color filament thing worked.

          1. We had a mouse problem. I sat out traps and found one caught by his tail one morning. So I released him in the sink and he ran into the drain before I could put in the plug and fill the sink with water.

            So I flipped on the garbage disposal switch….

  6. ” With the bonus of being installed below the sewer line, any maintenance will typically lead to a spill of raw sewage. It’s a peril this writer hasn’t experienced in 30 years of typical gravity toilet use; one must suspect few home maceration systems are quite so reliable.”

    Gravity sewage systems aren’t fun either. Have had to do my share because plumbers are both expensive and quite the trip to get here.

  7. Gross! How many of y’all, like me, read this article while sitting down for breakfast? And then how many of y’all continued to eat breakfast? Now we know the true HAD readers.

    1. It’s really not that bad :). I’ve been to a few sewage plants for inspection, the worst part is the head of works (where all the raw sewage comes in) but after a few minutes there you don’t even notice the smell anymore. The rest of the plant smells like the weird soapy smell coming from shower drains sometimes…

  8. I’ve seen a hot wheels, though pretty dinged up, come jiggling up an outfeed conveyor at a wastewater plant. Right after some dentures. Assume the two were unrelated. Kids will flush anything. Just yesterday my 18month old whizzed past me on the way to the bathroom – gleefully clutching a usb c adapter. Managed to intervene in that instance.

    1. Johnny Carson once had a guest that cleaned out sewage lines in a city (somewhere in Oregon, IIRC).
      He brought a collection of things he had found over the years, including a jar of dentures, and a suitcase full of marbles, as well as a pair of eyeglasses he had lost for a year.

        1. You’d be amazed what is collected in urban riverbeds.

          Back in the late 80’s after an El Nino rain event, I was walking along a beach and within a few yards had counted over 100 tennis balls, saw a whole pumpkin (this was in February), an assortment of used medical supplies, toys and dolls, and just a whole lot of garbage.

          Mother Nature used a week of rain to flush the toilet that the residents had made of the Los Angeles Basin.

  9. My grandfather had a macerator pump in an ammo can along with a 1″ garden hose and adaptors to attach it to a sewer cleanout, allows one to dump the black water tank without having to gravity feed it through a standard RV sewer hose, and allows you to dump it into a standard threaded cleanout plug if you don’t have a sewer connection near enough to the RV.

  10. I understand the massive cost of macerating all of our waste, but I have been suggesting that for decades.

    I contend that if all the garbage, waste, etc. were ground up before it was put into landfills or sewage plants, that Mother Nature would take care of decomposing it.

    Instead of compacting landfills down so no air reaches the waste, allow airflow and a lot of the stuff will decompose. Sure it will smell, but who gave developers the RIGHT to build next to a landfill?

    As for liquid waste, they already clean a lot of that and hasn’t there been discoveries over the years of things that will “eat” petrochemicals? I just saw a story recently about that.

    Yes, we are uncovering middens that are hundreds if not thousands of years old, but what do they have in common? They have all had dirt put over them cutting off oxygen. Is there any research on the extent of decomposition of what was buried? And if I’m not mistaken, they are usually in a big rush to catalog anything there because as soon as air hits it it starts to decompose fast.

    And all that BS about “running out of space” is idiotic. The entire population of the earth can stand shoulder to shoulder on Manhattan Island. Or be housed in condominiums built on about a quarter of the land mass of Georgia, USA. (I’d have to look up the numbers that Neal Boortz calculated.)

  11. How many times years ago did we see that ad in Pop Sci or Mechanix. “Basement toilet flushes up to overhead sewer or septic tank”. It would show a poor image of the stool but not the tank behind it. More recently I’ve seen ads showing the thing being behind it all.

    I saw one of those toilets at the curb once with the rear exit in my hood where the Pearl Creek became our first sewer, drainage shouldn’t have been a problem. Now our downtown is a mess of separating the storm and sanitary systems with orange safety cones and spray painted markings even on snow, signs of more digging to come. They used a tunnel boring machine to make a storage pipe right downtown just a block from the river.

  12. What I want to know is what the hell do I do when the power goes out if the macerater is run of the mains? I’m willing to use a candle during a blackout but I draw the line at using a cork!

    1. For light I would prefer LEDs. But a cork would become really dangerous if pressure builds up :-) So better have a generator ready or – if available – use a unit with an emergency handpump.

  13. My home was built below the sewage grade. There was no choice but to have one of these build into the floor of the basement whereby a 3′ round and 3′ deep tank would hold ALL liquids from the home until a float was tripped. After owning the home 6 months the float failed. And again 3 months later, and again. Eventually I realized I needed a contact-less method of determining the level of sewage/liquids to control the grinder pump. I looked into what sewage plants use – spoiler – NOT FLOATS. They use ultrasonic transducers to measure the level. This led me to design and build a small electrical box that used a 240vac contactor and was controlled by a Flowline ultrasonic sensor (programmable via USB). The entire parts list was probably $300-$400 but I have not had an issue again in YEARS. It is more complicated for sure, but no floats are used at all and so reliability has been 100%.

  14. For better or for worse, 20 years ago, when our small town decided everyone needed to on a central sewage system, they opted for a “pressure sewer”. In this system, each house has a macerator pump, and the outgoing sewage is pumped into a fairly small (couple inches) pipe that flows into a central collection point.

    While this makes for a much cheaper installation since all the main pipes could be directionally drilled (instead of excavating the entire town), I now have this pump sitting in my backyard that I’m paying electricity for and hope it doesn’t stop working and back up into my house. The town also has to replace them all every 15 years or so for a couple thousand bucks a pop since they wear out.

  15. As a plumber I took the conscious decision not to get involved with these things – aside fron occasionally fitting one. Saniflo are simply without equal in this field anywhere in the world. A French company…

    For people’s information, the worst thing for any macerator are those disinfectant / bleach blocks which sit in a plastic cage and hook onto the toilet rim. They all too often fall off and cause the blades to jam. The motor rarely burns out due to its controls but they’re a complete PIA.

  16. Anyone ever notice the sewage doesn’t smell as bad (from walking the streets when the vents effuse) in Europe (at least England, Netherlands and Germany)?

    I recall when I asked about the difference, other than possible different food and hygiene standards, that specifically they use enzymes more and even more enzymes in their clothes washing detergents.

    In the U.S. the industry literally just poisons everything with chemicals more-so or whatever has influenced the U.S. does.

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