I have a Kenmore He3T washer that has worked fine for just over a year. It came with a new drain hose with a 'hard U' for hooking on the standpipe and has had no problems up to this point. For the first time, I accidentally used standard soap (non HE) for about a dozen loads. This is when the problem started.

When the standpipe originally backed-up, I noticed quite a bit of lint coming up in the water. I also noticed sudsing.

I have been using HE soap for the past 6 loads and have stopped getting the sudsing and lint, but still get major water overflow. I was hoping the soap switch would fix it. It didn't.

I then ran my 3/8"x41" plumbing snake down the standpipe. I have 2" plumbing. The standpipe measures 20" to the p-trap, so I know I'm getting past it. A couple feet down the line, there is a 3' tall vent on the pipe (the machine is in an unfinished basement and doesn't vent up through the house to the roof). I have not tried to snake from the vent. That waste line then connects directly to the main out to the city sewer. The total distance of pipe between the laundry box to the 4" main is less than 15' and is on a dedicated line. No other sinks/toilets/showers in the house are having drain issues.

I've ran the machine through 'clean cycle' without any overflow. I've also ran at standard cycle without soup and clothes without any overflow. The overflow always starts at the spin cycle when I'm using even the most modest amount of HE soap.

In summary, I've switched soaps, snaked the p-trap, and ran half a dozen test cycles (without overflow)... but still get overflow when I try to do even a modest load of laundry. All my pipe is 2" from the wash and I managed to make it a year without any problems from this washer. Sorry for the long question. I've searched this forumn and have tried everything I've seen suggested.