Washing drain overflowing

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JWD

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I am trying to figure out why the laundry room drains are overflowing at one of the properties where I work. Every time the washer empties, the floor gets flooded. I suspect this has been going on long before I started here as I had to replace most of the studs in the wall from rot.
I had the line snaked to 50feet with no obstruction. I used a scope and saw no issues for 16ft. I've attached a couple photos.
My question: Could the P-trap in the drain line be too close causing the backflow? Any troubleshooting suggestions?
Thanks, much appreciated.
 

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If the washer drained at one time but doesn’t drain now, you have a pipe obstruction at some point.
 
Are you on city sewer or septic ?

Do you know if your washing machine drain connects to the city sewer if you are on city sewer ? Has your house ever been on a septic system?

There are houses here that were on septic at one time and then at a later date connected to city sewer. Sometimes they didn’t connect the washing machine drain to the septic tank so it never gets connected to city sewer. The washer had it own field line.
 
Are you on city sewer or septic ?

Do you know if your washing machine drain connects to the city sewer if you are on city sewer ? Has your house ever been on a septic system?

There are houses here that were on septic at one time and then at a later date connected to city sewer. Sometimes they didn’t connect the washing machine drain to the septic tank so it never gets connected to city sewer. The washer had it own field line.

It's an apartment complex. There is no obstruction for about 50 feet out. It was snaked and never hit anything I was told by the owner. When the washer drains, the water spills out almost immediately.
 
Well, it drains, but there is a lot spilling over. But yes, I get what you are saying, but we have looked into the obvious and cannot find an obstruction. When I put the washer fill line directly into the drain and turn the valve wide open, I can see the water outside moving freely through the access cap some 30 feet away without issue. The problem arises when the washers do their cycle and dump the water. It can't handle the volume and overflows. I don't see ventilation on these drains and they have the traps about 20-24 inches down into the drain. I was hoping to find something with a scope I bought but it is only 16 feet and there is nothing in that distance.
 
I can only speak to the past couple years since I have been here and it has always had this issue. I do know the wall studs were rotted from water damage, so it has been going on for some time. I have no idea beyond that, but one can assume it was working originally. building was built in 1970. But, there is no telling what has been done to the sewer lines or modifications etc. Apartment maintenance in general seems to draw people that just slap crap together. My background is construction, and when i saw these lines, I just knew it was nothing like the drain in my house I built in 2000. (plumbers did all the plumbing work) But, I have little experience with plumbing beyond real basic stuff so I came here in hopes of finding some troubleshooting assistance to try and figure this out because it is a bit confusing to me. We have been looking for an obstruction from day 1, but can't find anything.
 
if a true professional has cleaned the drain and it’s still giving you problems then a camera inspection is the next step.
 
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When you say the P-trap is "20-24 inches down into the drain", is that a measurement from the top of the standpipe to the bottom of the P-trap or to the weir, that is the outlet of the P-trap? And the minimum drain size for a washing machine standpipe is 2", which it looks like yours is.

At any rate, the standpipe has to be at least 18" above the P-trap weir, which apparently yours not above that minimum, and perhaps a little below. Depending on your governing code, the maximum standpipe height is 30" above the weir (UPC) or 42" (IPC).

Newer washing machines really pump out the water. As a fully open hose does not produce an overflow in your standpipe, it might be worth a try to maximize your standpipe height to your governing code's maximum. Another 12" to 24" might provide you with a surge volume to keep the washing machine from overflowing the standpipe. You could purchase just a couple of pipe components and not even glue them to see if that would help resolve the issue.

Now when you say, "I don't see ventilation on these drains", are you saying the washing machine drain piping doesn't have a vent after the P-trap? Vents are to keep downstream flows from siphoning the trap dry. However, for this standpipe situation, a vent close to the P-trap would allow water to flow up the vent a little before the water would come out of the standpipe. Note that this vent would have to be a true vent and NOT an AAV.
 
added a pic. 20-24 to the bottom of p-trap. As you can see, there have been modifications to the lines from the original. I might just redo the lines and crawl into the crawlspace to cut into the line to scope farther as well. Just going to have to keep at it.

The ventilation pipe, is just something I remember from when the plumbers roughed in the lines to my house years ago. The washer drain had an attached vent to the roof. Have no idea what code is etc. just remember it was something done.
 

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I always put a piece of pipe 30 inches long above the p-trap the a 45 then a piece of 6 inches.
never had trouble. but once a lady washed a bath mat in the washing machine and it got blocked up with lint.
 
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I’d drop my 75’ 3/8 “ cable down that stack or cut in a cleanout above the connections and run from there.

I can tell by the feel of the cable the condition of the drain.
 
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From the picture, it is obvious that you have several washing machine standpipes in a row. The two sharing the same drain and vent should be connected to the drain with a double sanitee instead of two sanitees stacked on top of each other. I can’t tell from the picture, but as SHEPLMBR said, “Looks under sized” and I think she is talking about the copper drain lines. All that piping needs to be 2”.

As I’ve said, newer washing machine really pump out the water. So, if the copper drain is smaller than 2”, that very well could be the problem. And if the standpipe is really only 20” from the bottom of the trap, then it does not meet the 18” minimum height of a standpipe above the P-trap weir.

I think I would do as you said; “…redo the lines (installing a double sanitee for those two adjacent standpipes) and crawl into the crawlspace to cut into the line to scope farther as well.” And I would be sure to make the standpipe is as high as you governing code allows; 30” or 42” above the P-trap weir, not the bottom of the P-trap.
 
Never install a pumped fixture on a sanitary cross.

Or some of the new toilets......
I see your point.

So, is it OK to stack two sanitees on top of each other like these are? That looks a little strange as the lower sanitee doesn't seem to be properly vented, as the short wet vent is vertical. How would you suggest these two standpipes be piped together?
 

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