We have a 16 year old Amana washing machine that is overflowing the drainstack at the end of the rinse spin. The water all flows out fine, it's just the suds at the end of the rinse that overflow.
Attempts we've tried that don't solve problem include:
+ had the drain line snaked 2x from the clean-out access just downstream from the p-trap.
+ extended the drainstack another 10" above where it was.
+ tried different brands of laundry detergent, and have used only minimal amount
+ had appliance repair guy over 2x and he's stumped.

It seems that the drainline is flowing fine, but the suds are not heavy enough to push the water through the trap.

It is suspected that the problem is not with the washer but in the drain line. My final solution for a similar problem was a chemical product called "Main Line Cleaner". We purchased it through Home Depot. It is primarily pure LYE which requires you to put it in at the extreme ends of the drain system & allow it to remain overnight with no drain usage. This means no toilet flushing, laundry, dishwasher,etc. In the morning, use HOT water at both ends of the drain to flush the "soft rubber" crud that has accumulated in the drain. This cleans the lines & any components along the way. In severe cases. A second treatment may be required. One treatment worked for us.

This sounds like a partially blocked trap to me. You said you snaked the line twice, but from a clean out after the trap. Try running a small drain snake down the stand pipe and through the trap. A toilet auger may or may not be long enough to reach the trap.
Assuming that this is a PVC stand pipe, you could even cut the pipe just above the trap, clean the trap and then reconnect the stand pipe.

For that matter you could probably cut out the trap and stand pipe and replace them both for about $20.

Thanks, hkstroud, for the suggestion about the partially blocked trap. When the drain line was snaked the second time, we disconnected drainstack from the trap and inspected the trap. The trap was clean & clear. Water drains fine through the trap. It was after that second snaking and inspection of the trap that we decided to extend the drainstack.

Thanks, bones252100. What was your "similar problem?" We don't have any other troubles with drainlines, and the water drains fine through the drainstack.

Well, if the trap is clear I suggest that you snake the line again. I know you won't think you should after already doing it twice. It is not that uncommon for a snake to go through a soft blockage and not clear it. Are you using a manual snake or a power one?

I noted that you said you have suds after draining of the rinse cycle. The rinse water should have almost no soap in it. To me that means there is some standing wash water in the pipes somewhere. Check to insure that the horizontal pipe between the washer stand pipe and drain stack is properly sloped.

Try running the washer with out any detergent in the wash cycle to test my logic.

A work around solution to this problem would be to simply seal the connection between the washer drain hose and the stand pipe. If you do that, you may or may not, come back later asking why you washer goes out of balance so often.

Just for clarity the pipe your hose hangs in is called a washer stand pipe. A drain or drain/vent stack is you main house drain and vent pipe.

I have another take on it. To days more powerful pumps discharge more then the system can handle. A found a solution 8 years and two washers ago. You make the closed one forcing the washer discharge through the system, You can do this by adding a washer compression fitting, (see Image) Or you can do what I did, Wrap the connection in duct tape. This has worked for years with no backups or overflows. Good luck, Tom

Hi Stumped

What kind of pipes are we talking about here? Are we talking galvanized pipe going into cast iron pipe... what? Let us know, OK?

Mark

Thanks all for the responses & clarifications.

Mark, the washer drain stack, trap, and vent stack is PVC pipe.

The water drains fine on the wash & rinse cycles. Without any detergent, it drains fine and produces minimal suds at the end of the rinse. Thus it doesn't seem to be a problem with the discharge volume / speed of water.

It is only the light suds that slowly pulse out of the drain hose, which seem too light to move the water through the trap, that overflow out of the washer drain stack. Last night we ran a washing machine cleaning solution through, and that generated some suds on the wash cycle, and they all drained out fine... until the end of the rinse spin. Then the light suds again overflowed.

I did try the duct tape work around a few days ago, and that worked in so far as the tape sealed the suds. Any gaps (of course) let little light bubbles slip through.

It still seems problematic that a) the washing machine produces the suds only at the end of the rinse spin; and b) the suds are light enough and just enough volume that a cup or two overflow the washer drain stack.

Sealing off the connection does work. You can search for other reasons and causes but sealing the connection is the only sure way to prevent a back up. Good luck. Tom

I'm the tech that addressed the problem on stumpedchumps washer. I've never in 30+ years of service seen this type of backup without the problem being in the drainline. Normally I can make a standpipe back up with a tub or 2 released back to back, but you can pump water for 4 or 5 full tubs with no back up. The wash water doesn't " foam back" but the spin time is shorter than the final spin after rinse, and it's at the very end of the spin that the foam back happens. It acutually spits foamy water all through the end of the spin while the pump is cavitating as one might expect with a poor rinse, but the machine will do the same thing if you refill the load and run a second rinse. Take out the clothes and the problem is solved. The only problem with sealing the gooseneck is siphoning in cooldown. It doesn't always happen but you may not be nearby if it does.

Hello Ken and welcome to AMHD.

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Take out the clothes and the problem is solved.

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That is an interesting observation.

You are the appliance technician. Any thought about how the clothes could possibly cause the machine to hold or retain the detergent until the rinse cycle? And if it some how did, why would the bubbles show up during the drain of the rinse cycle and not the drain of the wash cycle?

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I'm the tech that addressed the problem on stumpedchumps washer. I've never in 30+ years of service seen this type of backup without the problem being in the drainline.

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Stump a chump! Would you be the stump or the chump? Of course it's in the drain line. Mine was undersized at 1 1/2" and couldn't handle the volume.

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. I've never in 30+ years of service

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I'll call your 30 years and raise you 30 more. I've been in plumbing since I was 14 that would be in 1941. So don't try to roll over me with time in the trade. If you have a better solution let's have it. But I got to tell you. In all the 15 years I've been giving advice on sealing the hose connection I've NEVER had anyone complain that it didn't work. And now your solution. Cheers, Tom