Keep Your VacuFlush Toilet Working Properly

How To Keep Your VacuFlush Toilet Working Properly

VacuFlush toilets were all the rage years ago. Today I see many frustrated boaters replacing those aging systems with electric toilets because of vacuum leaks. I’ve been tempted myself.

After fifteen years of nursing my own VacuFlush toilets I have come to know and understand them pretty well. These  tips to keep your VacuFlush toilet working properly have kept my systems operating reliably and with few problems even after 30+ years in service.

So, here we go.

Understanding Your VacuFlush Toilet System

VacuFlush toilets rely on vacuum and there are three points of failure that plague these aging systems. The most common point of failure is the seal in the toilet bowl. The second most common point of failure is the seals at the vacuum pump which consists of 4 duckbill one way valves. And, finally the seal at the head of the vacuum tank where the vacuum off-on switch is installed.

VacuFlush Toilet System
VacuFlush Toilet System

Toilet Bowl Seal

The first problem I encountered with my toilets was the toilet bowl seal leaking vacuum. My first thought was that the seal is bad and needs to be replaced. And that’s what I did.

Many years later, when I have a leaking toilet bowl seal I do not replace it. These seals are made of pretty tough synthetic material and degrade very little over time.

So, why does this seal usually start leaking?

I call it calcification. The build up of a calcium like material on the surface of the ball valve and on the surface of the seals. This calcification creates a rough material on the mating surfaces that breaks the vacuum seal.

Duckbill Valves

These four one way valves are made of rubber. Rubber degrades slowly over time. Ad the calcification process that affects all parts in the system and you can see that these valves are the weakest links in this system.

The breakdown of these rubber valves will eventually require their replacement. But, some of our maintenance tips may prolong their life.

Vacuum Switch Seal

The vacuum switch is mounted on top of the vacuum tank. This is a pressure switch that turns the vacuum pump off and on. To do this there is a thin rubber seal between the interior of the tank and the switch that moves with the change of pressure in the tank.

This thin rubber seal wears out and will develop cracks that leak vacuum.

Maintenance Tips

The big enemy of the vacuum system is calcification. Eliminating calcium deposits will solve many of your problems. The way to avoid these problems is to dissolve the calcium.

1. Common white vinegar is the cure.

Regularly soaking the system in common white vinegar will breakdown the calcium deposits that have built up and break the vacuum seal. I do this about once a month. Flooding your toilet this way will also clean up a lot of the ugly, stinky stuff that accumulates in the area under the ball valve in the toilet.

To flood the system first turn off the water pressure and pump. Open the ball valve in the toilet and pour in the vinegar until it rises above the ball valve. Let it sit in there for an hour or two.

Scrub the ball valve and seal with a toilet brush as best you can. Get all the way into the lower chamber below the ball valve to clean up the yucky stuff. Close the ball valve, turn the water pressure and pump back on and flush the system.

If water is still being sucked out of the toilet bowl you may have to remove the toilet bowl from the pedestal to get full access to the ball valve and seal. This will probably be the case if you have never cleaned the system before.

Removing The Toilet Bowl

Removing the toilet bowl is pretty straight forward. Turn off the water and pump, remove the water supply line from the back of the toilet. Remove the cowling from around the pedestal. Then remove the band clamp connecting the bowl to the pedestal.

Set the bowl aside and you will find two flat seals sitting on top of the pedestal. Now clean and inspect the mating surface of the seal that contacts the ball valve. It is probably still good and simply needs to be cleaned of any remaining calcium deposits.

Now clean the ball valve. You will probably notice a calcium ring where the ball valve contacts the seal. Be careful not to scratch the surface of the ball valve. I have used a plastic scraper. But be very careful. If the surface is scratched it will have to be replaced.

Put everything back together being careful to get the ball valve seal back in just as it came out. There is a beveled edge on one side of the seal that mates up with the curvature of the valve.

Once you’ve completed this task your toilet bowl seal should be as good as new.

2. Making Your Maintenance Process Easier

Having to perform regular maintenance means that you have to shut off the water supply. Usually, that means shutting off the water supply to the whole boat. And, that you have to de-pressurize the entire system.

Wouldn’t it make a lot of sense to do what they do in every house? Have a valve on the water supply line to the toilet?

I went to the hardware store and picked up a couple simple in-line valves. One for each toilet. Now I simply shut the water off to each toilet when I perform my maintenance. The wife is happy because she can still use the sinks in the galley and the baths.

4. Making A Good Seal

I learned from a seasoned pro that if, when you depress the foot pedal to flush, you release it suddenly allowing it to snap back into position. I didn’t like the idea at first. But it makes a lot of sense.

The snap back ensures that the seal is set firmly in position. And it works.


These simple tips will help ensure a long and trouble free system. We’ll be discussing when and how to replace the second most trouble prone spot in the system, the duckbill valves.

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