# Freezing p-traps in plumbing system



## Donk4kyv (Dec 16, 2016)

My 150 y.o. farm house has no basement, only an open crawl space.  I recently had all the water pipes moved from snaking a jillion directions under the house so that they are now all above the floor, except for the short main supply line that runs from underground up through the floor. I have super-insulated that one and so far this has solved having to crawl under the house 3 or 4 times every winter to thaw frozen pipes, but both showers and the bathtub have a p-trap in the drain line, located under the floor in the crawl space, since there is no room for a trap above the floor. It got down to 18 degrees last night and one of the shower drains wouldn't flow this morning.  It thawed out a couple of hours later, so it was probably just a skim of ice on top of the trapped water, not frozen solid.

I could purchase a can of RV anti-freeze and pour some in the shower and tub drains whenever the temperature is predicted to drop to the low 20s or below, which should keep them from freezing.  Is that stuff safe for use with a septic tank?  I don't want to introduce anything into the septic system that will kill the bacteria. 


Don


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## begreen (Dec 16, 2016)

RV antifreeze should be ok, especially in the small quantities needed. Most bottles say safe for septic systems on them.


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## DickRussell (Dec 16, 2016)

Donk4kyv said:


> ..... but both showers and the bathtub have a p-trap in the drain line, located under the floor in the crawl space, since there is no room for a trap above the floor.



While using RV antifreeze (propylene glycol-based, not automotive ethylene-glycol-based) will be a good temporary solution for those bitter cold nights, I imagine you'd like a better long-term solution. It wouldn't take much to box in those p-traps under the floor, add insulation around and under the traps, and cover the box to keep out critters. That would let the slow heat leakage from the interior downward through the pipe to keep the contents above the freezing point. The same technique is used easily, on a temporary basis, to keep outside faucets from freezing on those few times a year when warm-climate locations get a cold spell. Just wrapping an old hand towel around the faucet, perhaps with a plastic bag tied around it to keep the towel dry, lets heat leakage from the interior along that very conductive pipe keep the water in the valve from freezing.


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## EatenByLimestone (Dec 17, 2016)

You could also plug in a heat tape on cold nights.


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## Highbeam (Dec 17, 2016)

This brings back memories. My first ewver plumbing leak was a frozen and burst trap under the bathtub hanging down into the ventilated crawlspace. The house had zero floor insulation.

I would take measures to prevent your crawlspace from ever freezing as well as insulating the traps.


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