I just plumbed in a new washing machine into our office closet, which backs our bathroom. There was previously a washer and dryer in there but the previous owners removed it and unhooked the drainage pipes. We plumbed in new ones today, and every time the washer drains, the water that drains from the washer backs up into our bathroom sink (fills the sink about half way) attatched is a crappy drawing of how we have plumbed it in... is there something wrong with the way we plumbed it? Or could one of my lines be partially clogged causeing the back flow? All the pvc piping is 1" 1/4 and is slightly slanted towards the floor from the sink, how it is suppose to be. I should probably install a p trap somewhere in the washer drain pipe to prevent sewer gases from coming into the house right? Is there something wrong with how I plumbed this in causeing it to backup to bathroom sink? Or could my pipes be slightly clogged causing the back pressure? Thanks for looking, and any help/advice is greatly appreciated! Thanks again!

You do need a trap for the sewer gas block, and you probably do have a clog, so you are right on both counts.
Washers back up easily because of the high volume all at once.

Hi Dewy:

Yeah....all kinds of issues here.

First, the STRAP is not allowed at the sink... must be a PTRAP.

Second, the washer also needs a PTRAP... as you thought.

Third, I see no vents here. In your case, you need a vent for the sink AND a vent for the washing machine. The vents connect together and then get connected into a VENT pipe (not the waste pipe) at a minimum of 42" off the finish floor in tyhen basement or at a minimum of 42" off the finish floor at a vent on the first floor, or up in the attic. At a minimum, you may be able to connect a mechanical vent (called an AAV), but they are illegal in most states, so that is up to you... best is to run individual vents, connect them together and run them into a main vent pipe. Be clear here, that vents must pitch back toward the drain and must connect into the main vent via an inverted fitting.

Finally, are you sure on the 1.25" pipe? If so, that pipe is way too small for a washing machine drain line. At a minimum, most states require an 1.5" minimum drain line...some require 2" as a minimum, so you are way undersized here.

In my opinion, you need to rip all this out and run everything properly with vents (see image below). If the drains back up after that then the drain is probably clogged at the stack pipe and will need to be cleaned.

Repipe this to the right size... should resolve the issues for you. Don't forget to install a full-size cleanout on this piping in case you need to snake the pipe now or in the future, OK?

Mark

Mark, I've never been clear about when a stack can't be drain and vent. Is this drawing incorrect because 2 vents don't tie into the stack 42" above the floor? I don't think I've ever had a house that was code if all these vents have to be added.

Just one more option to offer: You could also cut into that 4" stack with 4"x 2" "Y", install 2" trap and stand pipe... Milo

Milo... I think that is the ONLY option if that sink pipe is only 1.25"... :)

Joypulv, a waste stack can't be a vent IF anything drains into the pipe from above. In this case here, Dewy has the entire house draining into the waste stack so he/she can't connect the vent back into the waste stack until he/she is at a minimum six inches ABOVE THE HIGHEST FIXTURE IN THE HOME... then the waste stack becomes a vent stack and goes out the roof.

Further, you may not have seen as many vents as we talk about here sometimes as codes do differ from state to state... some allow WET VENTING (less vents needed), but most require individual vents at each fixture (as described above). In Dewy's case, however, a vent is required for both fixtures because no state that I know of allows a washing machine to wet vent a sink or toilet so the sink and washer both need individual vents.

I hope that made sense. Let me know if you want to discuss more... always a pleasure!

Mark

Well explained Mark... Sorry, the system would not allow me to rate your excellent answer