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droy 01-23-2008 05:42 PM

Water from sink backs up in stack pipe.
I removed my gross laundry tub and washing machine drain pipe that hangs in the tub and replaced them with a sink in a counter top, plumbed the sink and the washing machine into the existing 3" drain that the laundry tub was plumbed into. I put in two traps, one on the washer is lower than the one on the sink, then I put in an air stack on the straight pipe that goes into the drain. It didn't have an air vent before but i figured it would be a good idea with the washer outlet being placed into the waste pipe. When I fill the sink and let it go down the drain (with the washer not running) the water fills up the air stack until its even with the sink water and then they both seep down the drain over 1 minute or so. The laundry tub used to drain super fast, so I know that I screwed up something. Did I not make the two traps at different enough heights? The sink drain has to go through both traps to drain. The washer only goes through the low one.

Ron The Plumber 01-23-2008 08:35 PM

Having a hard time seeing this, can you make a drawing and post it for me to see it.

47_47 01-24-2008 12:49 PM


Originally Posted by droy (Post 91349)
The sink drain has to go through both traps to drain. The washer only goes through the low one.

I am not a plumber, but I believe you should not have a drain going through two traps.

almostdone 01-24-2008 02:13 PM

Double traps are against most plumbing codes and this is one of the reasons. It should be repiped and when this is done you can check the condition of the inside of the pipes to determine if snaking or high pressure water jetting is necessary also.

almostdone 01-24-2008 02:31 PM

Its hard to picture exactly what you have. You should have came out of the 3" with 3"x2" spigot then a 45 to get to the horizontal then a 2" wye with one branch going to the sink with its own drum trap and the other branch of the wye going to your laundry stand pipe with its own drum trap. You would obviously reduce to 1-1/2" coming out of the wye to accomodate the drum traps. With drum traps you should not need any venting.

Marlin 01-24-2008 06:39 PM

What you have there is commonly known as a mess. Double trapping is neither allowed nor good practice. Take a picture of what you have and we'll get it sorted out.

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