Changing S traps to P traps?


Old 08-07-07, 11:35 AM
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Join Date: Jul 2007
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Changing S traps to P traps?

My wife and I recently purchased a handy man's special. The house was built in the late 1800's which means that we are working with several generations of repairs and additions.

One of the bathrooms is on the first floor with an unfinished basement, making all the drainage pipes accessible. The sink and tub/shower both have s-traps with inadequate or non-existent venting. Ideally, the whole system needs to be replaced. But until i have the time and money, I am hoping to put a band-aid on it.

I am wondering if I can make the s-traps into p-traps by extending the first downward section of the pipe. Then I would add the p-trap a little lower the bit would in a traditional setup. Would it be a problem to have the drain pipe so long? Would the pipe be draining too fast? I would also add an AAV for now. See the drawing here:

The toilet in this bathroom is another matter and i think it will have to take a picture of that one. it is too hard to describe what is happening there.

I should mention that the supply lines needed to be replaced and I just finished them yesterday. So i have not had the chance to really run water through the drainage lines to test for gurgling sounds or sewer smells. (this has been my first real encounter with plumbing and i am proud to say that, after running all new supply lines, i only had a couple leaks at the compression joints. all my solder joints were just fine.)

Any advice or suggestions would be great.

Thanks for the help.
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Old 08-07-07, 02:41 PM
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I would leave the traps above the floor line. Too much influx of water into the trap can also clear the trap and not allow any water to remain for a seal. Why not come off the lateral line before it drops through the floor and fit in the AAV at that point. You can do likewise on the tub if you can get the AAV above the trap.
Old 08-07-07, 04:49 PM
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Thanks for the reply.

I think i can do as you suggest for the sink. But there is not a whole lot of room behind the sink. the p trap would have to go right into a t . . . it would end up looking like an s trap with vent on the top of the second turn. would that be ok or would that drain too quickly?

for the tub, the only access to the drain is from the basement, so there really is no way to keep the trap above the floor line. but i could try to keep it between the floor joists with just enough room for an AAV.

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