Help with washer standpipe overflow

[Quan Vo]

I am having an issue with water overflow on the washer standpipe. We clogged and there wasn't anything blocking the pipe. I tested with the water supply hose for a few mins and ran into no issue. However, depends on the wash cycle, the volume of water discharged from the washer causing overflow. I recently moved the standpipe from the other wall to this new location and it happens. We weren't sure if this has happened before or not. I used 2" PVC for most everything, the standpipe height is 2 feet, but the main drain is old and only 1 1/2". I appreciate any help and advice. I suspected the discharged water is too much for the main drain to handle? Also, I added a 90 degree elbow to relocate the pipe to this wall, it used to be on the right-hand sidewall, where the purple foam board located, wonder this addition would slow down the flow?

 

[Mliu]

Show us the rest of the drain, especially the area where the old pipe was before you relocated the standpipe. Also, show us the new 90° elbow. Did you use a proper standard or long-radius drain elbow or did you use a short-radius vent elbow?

 

[Sponsor]

 

[Mliu]

Also, International Plumbing Code prohibits the reduction in size of drain pipe:

704.2 Change in Size
The size of the drainage piping shall not be reduced in size in the direction of the flow.
​

Presumably, the UPC has a similar prohibition, although I don't know the specific section to reference.

 

[Quan Vo]

Hi @mliu thanks for responding.

Here is the old pipe position, and the 90 elbow that I am using. Unfortunately, the basement is completely finished and the bathroom is next to this, so there is no access to see the vent (if there is one).

 

[Mliu]

Is that a Fernco 1-1/2" coupling elbow?

Your first problem is that you added a 2" standpipe and P-trap feeding into the 1-1/2" drain. I'm sure you thought that would improve flow but, in addition to being a code violation, it's likely contributing to your backup. As the water hits that reducing coupling, it creates a lot of back-pressure that slows down the flow at that point. If you kept the pipe at 1-1/2", then the flow velocity will be established in the standpipe and should continue downstream without much back-pressure.

I'd replace that standpipe, trap, and coupler with 1-1/2" and see if that solves your problem.

 

[Quan Vo]

Hi @mliu

I did that first and ran into the same issue, see the pic that used 1 1/2 pipe and p trap before replacing with 2" pipe.

And yes it's the Fernco 1-1/2" coupling elbow

 

[Mliu]

Did the original standpipe work without overflowing?

Is the washing machine the same as before?

 

[Quan Vo]

It is the same washer, and we barely see the issue before. We saw some in the past bu suspected that was from the washer and it was inconsistent but didn’t see much water on the floor before.

 

[Mliu]

When you say "barely see the issue before" and "didn't see much water on the floor before" that means that you did have this problem, only it wasn't as severe before. There should never have been any overflow from the drain.

I'm guessing that the old drain was just barely able to handle the output from your washing machine, and when you moved the drain, that was enough to make it overflow every time (instead of just a little occasionally).

So now the question is, what was the problem with your original drain. Perhaps it just needs cleaning. But it may be worthwhile to have someone run an inspection camera down the drain to see what's going on since you don't even know where the vent is or how it's plumbed downstream.

 

[Jadziedzic]

Suggest you take a picture of the area where the drain pipe the washer drains into enters the floor and post that here. If the original drain pipe (which looks to be copper) feeds into a larger hub then you could replace the entire run with 2" PVC. A picture would also confirm if the original drain was properly vented.

 

[Quan Vo]

Unfortunately, I can't access to see the drain pipe enters the floor since this basement is all finished. There is a bathroom next to the laundry (all closed up) I couldn't access the vent so I am not sure if it's properly vented or not, is it possible to add another vent within the laundry plumbing (without actually going through the roof) I am thinking to connect the washer hose to the Y and extend the standpipe (which becomes a vent) or add a Air Admittance Valves somewhere (after the P trap) to support it. Is it possible?

 

[Quan Vo]

When you say "barely see the issue before" and "didn't see much water on the floor before" that means that you did have this problem, only it wasn't as severe before. There should never have been any overflow from the drain.

I'm guessing that the old drain was just barely able to handle the output from your washing machine, and when you moved the drain, that was enough to make it overflow every time (instead of just a little occasionally).

So now the question is, what was the problem with your original drain. Perhaps it just needs cleaning. But it may be worthwhile to have someone run an inspection camera down the drain to see what's going on since you don't even know where the vent is or how it's plumbed downstream.

There wasn't any problem with the original pipe, I am relocating them just because we remodel the laundry room.

 

[Tuttles Revenge]

The old method of draining a clothes washer into a sink that then drains through a 1.5" drain is the way to go. The sink will hold the volume of water while the drain slowly drains that volume.

Also, those style rubber fittings all have reductions in their internal diameters. So an 1.5" 90.. is really 1.25". Remove those and replace with PVC fittings to increase the amount of flow. You still won't be able to drain the washer down the 1.5" drain without a reservoir.