Poopers - vacuum toilets

Why do some ships use vacuum toilets? They always have problems and seem like such a hassle. The only argument that I’ve heard for them is that they use less water, but you end up flushing 3 times to make sure they don’t clog. What gives? Seems a lot easier to maybe a replace a toilet and wax ring rather than spending money on cheap plastic parts and man power


Warning in the passenger bathrooms of a large cruise ship >>>

In one of the bathrooms at Coast Guard HQ:


If designed correctly or after the kinks have been worked out after new construction, I prefer the vacuum toilets. Thats because you have a set of pumps actively sucking the flow toward the tank. Old school, gravity flow to the tank systems have problems on larger vessels & installations where the toilet water, toilet paper & shit has to travel long distances to the MSD plant. Yes, the flush assemblies can be a pain but I think working on them is easier & cleaner than working in a room with a couple of inches of shit water on the deck.

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the best toilet sign on a boat is…

“Anything you put in the toilet besides toilet paper that you didnt eat will be served up for dinner so you can have another go”


I could tell some real horror stories about a gravity flow system on the SEA SKIMMER. . . .

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As a C/E of a converted RO/RO to RO/RO/LO/LO US government REPO ship with both gravity(original ship) and vacuum(converted) toilet systems.
The number 1 advantage to vacuum is you can literally make Sh!t flow uphill. Think about it on a cruise ship, having to make all the poop piping have a fall.
The number 1 disadvantage to a vacuum system is that the chemical compounds found in pee precipitate out of the pee under a vacuum and coat the interiors of the piping. After a few years a 2 inch diameter pipe becomes a 1 inch diameter pipe. Learned this the hard way. Phosphoric acid removes this but the resulting sludge become a peanut butter consistency that ends up in the V1 tank, learned that the hard way too.


And even worse, what was flexible hose becomes rigid. A job for the n00bs was taking lengths of head hose out and beating it against a tree to get all that stuff out.
I am not sure how this would work on a cruise ship, but the cure on a boat was to send a quart of vinegar down the head every couple of months to dissolve the deposits. Actually speaking of ships, I didn’t know vacuum systems scaled up like that. Vacu-Flush is a big deal for boats with limited holding tank space, you get 2-3 times more endurance between pumpouts than with the old fashioned heads at the cost of wiring, pumps, and so on.

Back when the company wanted contract cuts(wages) from the Engineers the Union officials called me into the office for a chat, they wanted to know what was so special about these ships, they had never visited in the 15 years of operation. I explained 6 cranes, 23 doors, stern ramp, yada yada yada, but the only thing that got their understanding was 87 toilets, 65 of them vacuum type.

I never worked with the vacuum toilets when I was on tugs & ATB’s. The gravity flow systems worked out pretty well on those old boats because there weren’t many heads & the superstructures were compact making the flow very reasonable. The last larger vessel I worked on that had gravity flow was a nightmare concerning toilets though. Every level had a designated shopvac in a closet somewhere just for shit water. Don’t miss that at all.

We drop descaling packets down every vacuum toilet weekly. Makes a huge difference.



My comment about the phosphoric acid was something we did back maybe 15 years ago. when we discovered the the flow piping diameter on the vacuum system had decreased from 2 inches to about 1 inch and a healthy wad of T paper would plug it up, I called Enviro-Vac the manufacturer of the system. I explained my issue to the Engineer on the phone. He had me on speaker so all the Engineers in the office could hear me. He asked how long we had the system running without treating it, I told him 15 years and you could hear the room explode in laughter. The options were explained in detail, the Navy uses a high pressure washing process, then there was the phosphoric acid method. I got 55 gallons of high grade phosphoric acid and treated the system during a yard period, Now vacuum systems are much more widespread and they make drop in the bowl preventive treatments.

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If coated piping is used for vacuum toilets they are relatively trouble free as long as nothing goes into them but a little toilet paper and bodily fluids.

@steamce: that is some golden information right there. Thank you. No pun intended lol

We used a chemical injection system on newer vessels mounted in the access panels between two toilets at the top of each stack. The chemical I recall is called Uriclean, which was just phosphoric acid and some other things. Seemed to work fairly well at reducing scale and buildup but occasionally the acid would eat through the fittings and then you have a vacuum leak to find.

Vacuum leaks and flush mechanisms might be preferable to gravity sewage floods. Though I could tell some stories about unblocking vacuum lines with hacksaws, power snakes, and compressed air…still haunts me to this day.

On older vessels l like MSC’s T-AO’s those pipes were so built up that like someone mentioned what was once a two inch pipe could be less than half that with the rest a solid scale. Plus there were some unfortunately placed short-radius 90-deg elbows on those ships that were a nightmare.

On a vacuum toilet if only bodily excretions and single ply toilet paper are deposited, in theory the force of the initial flush suction is meant to instantly create a slurry that can flow all the way down to the tank. Some older systems draw suction on a vacuum tank but the newer ones I’ve seen the pumps are vacuum/macerators that do dual duty and you can eliminate the vacuum collection tank. Of course they had a plexiglas lens over the pump end that makes it look like a chocolate slushy machine.

Personally I kind of liked the vac tank for leak finding/clog breaking. Close off the tank, pull it down to near perfect vacuum, then slam open one leg and shock it!

I guess i’ve seen the worst of both systems … guess i’ll stick with the sea water flush one.

I experienced both types in my career and I prefer the gravity flush simply because I got nervous every time a a vacuum toilet activated. Now that I am retired I enjoy the sound of water rushing into the toilet and sending my crap away. No longer do I have to worry if my poo does not disappear quickly and my engineers may have to discover why. On the other hand I still travel quite a bit and every time I use the toilet on a plane and hear the vacuum it brings back bad memories of all manner of things plugging up the system. The retired deck guys I know are not blessed with memories such as this and neither do they understand the humor.

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Speaking of deck guys and humor, a fun trick that only works on vacuum toilets is to swap the flush button tubes in an access cabinet for two toilets for side by side cabins. That way when one guy tries to flush his toilet he hears the next cabin over flush but his deposit sticks around. Confused two birds with one stone!


Recently on the way home I was woken by the sound of flight attendants fighting a flooding toilet. I felt absolutely no guilt in turning to the other side & going back to sleep. Over the years I’ve heard the announcements over the intercom requesting anyone with medical training to press the flight attendant button, never for help with a vacuum toilet.


On ferries on the Dover - Calais run our biggest blocker of vacuum toilets was passports. Illegal immigrants threw them away so that they could claim that they were stateless.