Monday, December 5, 2022


Our bathroom sink P-trap froze!


RV Doctor

Dear Gary,
We were recently caught in an arctic freeze. We went to ready our RV today for a trip next week and found our sink drain P-trap in the bathroom frozen shut. We had to pour hot water down the sink in order to melt what appeared to be a solid block of ice. My husband tried to take apart the P-trap at the joint, but it would not budge.

Was anything damaged by this? How can we avoid this in the future? We don’t winterize the RV since we use it during the winter some. We’re sure it had something to do with the recent very cold weather system that came through. Thanks for your helpful hints! —Mary D.

Dear Mary,
Wow! You were in some seriously cold weather! I have one word for you: Florida! Seriously though, I’m sure many P-traps probably froze during the recent cold weather. Unless proper precautions are taken, it probably happens more often than most people realize!

One of the problems with the standard P-trap in an RV is that they require regular maintenance. Unlike P-traps in residential or commercial sink drainage systems, the RV P-trap is not used as regularly; therefore, diligence on the RVer’s part is necessary. Some of the drawbacks to RVs equipped with standard, run-of-the-mill traps is that the water lock must be maintained at all times. Without that sealing water lock, odors from the holding tanks can rise up and into the living portions of the RV.

And keep in mind, it is code-compliant (and fairly common) for some sinks to be plumbed to the black, solid waste holding tank. So odors from either tank may have a direct conduit to the interior of the RV if you do not keep a watchful eye on the level of the water in each trap. (How many of you with RVs equipped with a combo washer/dryer have ever checked the P-trap associated with the washing machine drain?)

Because we don’t use RV sinks as often as the sinks in our homes, it’s also plausible for the water in the P-trap to lose its sealing ability due to common evaporation. Also, as RVs round corners, especially on curvy mountain declines, the water in the trap can be swished out of the trap, again creating that free pathway for odors to enter the living areas.

I’ve even seen instances where the lavatory sink was plumbed to the toilet holding tank and simply flushing the toilet caused the water in the trap to be siphoned out of it, enough to negate the water lock.

For RVers who use the coach during cold weather, it’s not a bad idea to pour 1/4 cup of RV antifreeze down each sink drain every few days to ensure the water does not freeze, if that sink happens to sit idle during a cold snap. As an alternative, windshield washer fluid, which is less expensive in most locales, can be used instead of RV antifreeze.

But to be 100% worry-free, and 100% odor-free, I recommend replacing all the RV P-traps with a HepvO waterless sanitary valve. You’ve probably heard me mention the HepvO in a video or seminar somewhere before, but I can’t say enough good things about this unique plumbing device. It is 100% maintenance free and eliminates the possibility of holding tank odors from ever entering the living space of the RV. It also provides for more storage space under the sink since it can be installed vertically or horizontally and can be positioned as high up as the sink will allow. It’s hard to argue against any serious RVer who can appreciate the positive attributes of the HepvO. Another good thing is that it is easily installed by the average handyman. I’d encourage you to take a look at my video regarding the HepvO valve. You can view it here.

I doubt the severe cold snap you encountered damaged anything in the drainage system, unless, of course, you see leaks when running water through that drain. But I can guarantee you’ll never have a freezing problem again, since the HepvO waterless sanitary valve is not dependent on a water lock to prevent odors from coming into the RV, hence the “waterless” part of its name. Check it out here or at 1-1/4 inch trap, or 1-1/2 inch trap.

gary-736Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.


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Anne Courcelle
3 years ago

Dear Gary, can you help me with a problem, I amhaving trouble with myfurnace, the fan and air conditioner work but the furnace will not come on, I checked the fuses and they are fine, furnace just won’t click in.

Doug W/ND
3 years ago

Our motorhome goes into storage so we don’t use it during freezing weather in ND. I remove the traps and place them in the sinks as a reminder! I also plug the line from the holding tanks and have had no problems with odors in 20 years. Additionally, with the tub/shower trap, I fill it with Rv antifreeze and haven’t lost a trap yet – down to -35 deg. F. I also put antifreeze in the holding tanks and the pump, potable water tank and water heater; and I remove the flush valve and drain the toilet.

Arlene Wood
5 years ago

We live full time in our 32 ft, Coachmen Leprechaun, and we have a problem with the bathroom sink clogging and backing up into the shower, We are very careful to clean all dishes before washing them and we use a drain cleaner each time we dump. Any suggestions.

3 years ago
Reply to  Arlene Wood

Pour vinegar down then weekly. It will help dissolve hair and other debris.

Fred Coston
3 years ago
Reply to  rvgrandma

Try some rock salt , like you use on sidewalks . It will not harm the pvc pipe . Not sure about chemicals in the tank you may use
It melts ice on roofing edge , and sidewalks .may need to replace a small amount every night

Gregory Illes
3 years ago

I have these installed in my motorhome kitchen and bathroom sinks, and they are terrific. I can highly recommend. Also, an additional benefit is that they don’t tend to accumulate skanky crud because there’s no standing water. Lastly, they take up less space, which is always at a premium in RV’s.

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