Hello - my washing machine discharge water is overflowing from the box in the wall where the valves and discharge line is mounted. My plumbing lines run as follows: from the box in the wall, it goes down vertically about 15 inches, 90 degree elbow to the right , runs horizontally about 24 inches, 90 degree elbow down, runs about 18 inches down vertically to a 90 degree elbow into a trap, then another 90 degree elbow, then runs into the sump pump box (in basement). All of the drain lines in the wall are 1 1/2 PVC. If you slowly pour water down the drain, it's fine, but with the volume the washing machine puts out, the water backs up and overflows. Any help is GREATLY appreciated.

I'm no expert... just a simple single mom... but mine did the same thing.. first.. can you get rid of some of the elbows.. not sure if that's possible.. or if it will work..
My problem was that it was not sealed tight enough... my solution... Lots and lots of duct tape... I pushed the hose from the washer down as far as I could... then Lots and Lots of duct tape... Hope that works... Good Luck... p.s... did I mention I'm not an expert...

Your stand pipe should go straight up. You have too many 90's preventing water from discharging as it should. Was that always happening or did it just started ?

You will probably have to snake your drain. Hope you have a clean out close by.

I just installed this so it is new. What is the stand pipe - sorry for my elementary questions! I also do not have a vent except for the small little vent on the pump/tank cover.

What size and type of pipe did you use for this drain? Lots of questions I know but where do you live and where does the sump discharge to?

I used 1 1/2 inch PVC for the drain. The washer is in the basement so all of the discharge water is draining into a Water Ace Sink pump System. The discharge from the pump system goes up about 8 feet into the main 3 in drain line for the house. I have a check valave installed about a foot away from the entrance into the main drain line.

I am in the Atlanta area.

There is a system installing W/M discharge. You have to have about 36" tall, 2" diameter stand pipe to absorb all the discharging water. It should be straight piece of pipe. Now, it will work with 1 1/2" pipe but pipe has to be straight up - no 90's. The way you described it, it seems like you have 3 - 90 degree turns on the down run before the pipe reaches trap. Undersized pipe and 3 sharp bends will inhibit water drainage. I am positive, this is the main reason for back up.

Is the wall still open ?

There is a system installing W/M discharge. You have to have about 36" tall, 2" diameter stand pipe to absorb all the discharging water. It should be straight piece of pipe. Now, it will work with 1 1/2" pipe but pipe has to be straight up - no 90's. The way you described it, it seems like you have 3 - 90 degree turns on the down run before the pipe reaches trap. Undersized pipe and 3 sharp bends will inhibit water drainage. I am positive, this is the main reason for back up.

Is the wall still open ?

No, but that's not a problem. I anticipated I would need to tear the sheetrock out to fix this. What about the lack of a vent except the one that is on the sump pump cover?

Ok, Sump pump needs its dedicated vent. W/M needs to be vented as well - unless it is very close to the pump.

Your main problem is that you don't have enough room in the pipe to absorb all the volume. Today's w/m's have very rapid discharge do they need 2" pipe.

Some plumbers in this Forum would suggest that you could seal/secure end of w/m hose to the drain pipe with special coupling so it prevents water from overflowing. It is a solution that I don't like but have to admit it may work for you.

Thanks for your insight. How close does the WM need to be to the sump pump to eliminate the need for a vent? Adding a vent may be a problem because of room restrictions.

Instead of running vent all the way through the roof, you can install retrofit vent, called Air Admittance Vent. It is not allowed in all States. But if your job is not being inspected, you could install it to help the drainage.

Sorry to say, but the undersized pipes and the 90 bends will still leave you with the problem...