I'm am moving my washer into an old closet directly behind the guest bathroom. I have easy access to water there and a 1 1/2 drain pipe from sink going into main 4" vertical drain pipe about 2 feet away. Can I "T" into the vertical sloping 1 1/2 drain line for my washer drain standpipe? Will the standpipe need a P trap prior to going into the vertical drain line?

I've read lots of problems with washer drain backups and would like to avoid that ahead of time. I can attach a picture if its possible on this site or could email one if someone could give me some advice.
Thanks.
John

You should tap into vertical 4" pipe with 2" San T ( or some prefer 4x2 Y ). Leave sink drain alone since it is only 1 1/2" pipe. You will need 2" trap and minimum of 30" of stand pipe for washer. Since you are only inches away from 4" stack, you can get away with not using vent.

Thanks for the quick answer. Ideally, 2" into main 4" would be the best solution, but tapping into the 4" main will be tough. It's close, actually about 3 1/2' now that I've looked closer, but its behind the walls between the two tubs in the two bathrooms (they are at right angles to each other). I can see the 4" through a small access panel behind one of the bathtubs.

The 1 1/2 horizontal sink drain line is about 18" from the floor and runs through 3 studs before hitting the 4" pipe. Would it be possible to run the new washer standpipe straight down below the 1 1/2 sink horizontal drain pipe, install "P" trap, then tap into 1 1/2 horizontal pipe from below between sink p-trap and 4" main? Hope this makes sense to you.

I've attached a couple of pics so you can see what I'm looking at. Is it possible without tapping into the mainline?
Thanks again.
John

Thanks. I did run 2" over to the 3" (not 4" like I first stated) vertical stack. Took a little planning, but came out well and hopefully all within code. My standpipe is 30", p-trap within 12" of floor, and a vertical run of 44" to vertical stack, so don't need extra venting.

Please let me know if anyone sees a problem.
Thanks.
John

Your works looks nice and clean...

You are not stating your location. Let's say in my region of operation, we have to install vent on every fixture regardless how far away it is from main line. However, looking at your existing sink drain , it appears to me it runs directly to main stack; therefore, I am assuming you will be fine with your Code. Let's see what other plumbers in this forum have to say...

Thank Milo. I'm in NW Florida.