DIY: Making a Commercial Toilet work with Residential plumbing

DIY: Making a Commercial Toilet work with Residential Plumbing

Yes, it can be done, but it takes a bit of ingenuity to make it happen.

Background: my mother was having the basement in her house completely redone with all new concrete, plumbing, etc, so we decided to have an extra bathroom plumbed in. I had always wanted a commercial flush toilet, so I bought that for her, and the basement remodelers did the installation. I knew that an expansion tank would be needed, and a one-way valve, so they put those in. However, even with those items, it never really flushed very well. The first improvement I made was to increase the size of the expansion tank, which helped a little bit, but not enough.

Here’s the current state:

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I did some research, and I learned that these toilets need volume, lots of water volume in order to make them work, something that my residential plumbing did not have. Additionally, the way the plumbers ran the piping, they had a serious restriction after the one-way valve and before the toilet, so that wasn’t helping anything.

Additionally, the expansion tank was oriented on it’s side, which probably was decreasing it’s performance. Even if the tank was oriented vertically, there was still the piping restriction.

Time to do a complete re-evaluation of the system and come up with something better.

Since volume is the driving factor, I wanted to have an expansion chamber with a large opening, and have that located as close to the toilet as possible, with as large of piping as possible. Expansion tanks available just didn’t have a very large opening, 3/4” NPT seemed to be about the max.

I looked at the self-contained pressure flush toilets that are available, thinking that maybe that system could retrofitted onto this…. well, they all seemed proprietary, but one thing I noticed is that it was really just a sealed vessel with water filling it… maybe that design could be modified.

So I decided to make my own. I wanted to use ~4” PVC pipe and make a vertical chamber to hold the water, if it was sealed at the top, the air that is in it would be pressurized by the water when it filled the chamber, acting just like the pressure flush toilets already available.

I did some research on PVC, and the commonly available cellular foam is NOT pressure rated. After a bit more searching on, I was able to find some large (4”) pipe, PVC, that was pressure rated to 220 PSI. More than sufficient, since water pressure is ~45-65 PSI.

So here’s the plan I came up with:


Now to buy the fittings, and see if I could make this work while I was home on vacation.

Buying fittings is always a pain, as finding the fittings you want can be a challenge, and sometimes a plan has to be modified slightly based on what’s available, but I finally had what I hoped would be all of the right ones. Now to implement!

My first step was to disassemble the current setup, and then test fit all of the new fittings to see if I had all of the correct fittings.

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I didn’t have quite the right fittings, so I had to scrounge some in the shop, and fortunately, I was able to find some that works, which were the 2 brass ones to go from 1” female to 1” female. Whew, now I could start gluing it up. After letting the PVC glue dry for several hours, I assembled it together, ready for the first trial.


It works!!!

Unfortunately, after a short time, I noticed some tiny leaks in the PCV fittings. I hadn’t gotten enough glue in them to adequately seal them. I disassembled it, carefully did some cutting, and reglued them, which helped, but still wasn’t enough. Additionally, I had a metal male fitting going into a female PVC fitting, which is a bad scenario as the PVC can crack over time due to the pressure. It is recommended that only male PVC be threaded into female metal fittings, as then the PVC is under compression.

But, it proved that the design would work, and I just needed to buy some additional PVC fittings, some heavy duty PVC cement, and re-do that portion of the work.

A week later, I had the new fittings, the heavy duty glue, and it was time for round 2 of this! This time I made sure I had lots of glue on the fittings before I pushed and twisted them together for a good seal.

The new fittings allowed me to make the pipe slightly longer, which increased the volume of water slightly, not a huge change, but every little bit helps. Total volume in the pipe chamber is 2.6 gals, but a small amount is taken up by the air that is pressurized, so total available for a flush is around 2 gals.

Here’s the PVC cement comparison, and the pipe joint sealer:


After letting the glue cure for several hours, I put it all back together.

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Now for the final test:

Here’s what the water pressure looks like during the flush:


Disclaimer: I am not a professional plumber, and if you choose to do this for yourself, I am not responsible for your incompetence or stupidity in how you implement this. This system may not be in compliance with local codes, you are responsible for checking and certifying. This worked for me, but it might not work for you, I am not liable in any shape or form. You are responsible for your own actions and results.


PS: I hate to have to have this kind of a disclaimer, but there’s just too many stupid people out there that don’t take responsibility for their own actions, and I refuse to be liable for someone else being stupid. If you aren’t comfortable doing this yourself, and being responsible for the possible failures, then hire a professional and let them be liable.