i just installed a p trap under my drain in a new shower, previously a tub, water will not flow out of the trap and i have grade, no blockage anywhere, what's happening?

Fr_Chuck

it has to flow, you are saying the water is just not going though the trap, backing up into the shower ?

jbasso

right, it just overflows back into the shower

Fr_Chuck

pure gravity would cause it to flow down hill. So there has to be a blockage somewhere if this is happening. have you opened the pipe on the P trap and followed to where the blockage is happening. pure gravity and water flow forces the water to follow to the losest level ( which is why drains work)

jbasso

we ended up cutting out the trap and put a hose in the line, no blocks, tomorrow we will use a camera/snake and look for venting problem, plumber was stumped when the line was clear and when we reattached the trap again it wouldn't allow water to flow through it

Fr_Chuck

the trap must be causing a vaccum of some sort not allowing the water to go out. Is there a vent on that line ?

jbasso

i would have thought so since we just tore out a bathtub, wouldn't that have been vented?

Fr_Chuck

should have and is, are not always the same thing. Back in the day when I actually did some real plumbing, I did alot of older homes that had so much patch work, no code plumbing it was a sin.
if this is a PVC trap, they are only a couple of dollars, have you considered using a different design, also if yours has a clean out on it, have you opened the clean out a bit and tried to break any caccum that may be happening.

I am not up on all the fancy things, I am sure one of the "real" plumbers will come on here, I do actually have my license, but it was grandfathered in years ago.

jbasso

thanks for your input, it is the cheap pvc type and doesn't have a clean out so we couldn't experiment with it, will let you know what they find tomorrow concerning the vent, it's all greek to me

Fr_Chuck

Yes, I just put one in on my washing machine drain, for some reason, it did not have one. Getting to old and fat to be in the crawl space any longer.