I wasn't sure, so I copied this over from the plumbing forum.

First let me say how impressed I am with this site and your willingness to help DIY'ers.

For some background;
We have a 30+yr old house designed and built by an old school DIY'er. Suffice it to say we have discovered some interesting engineering. He obviously had a good supply of 2" drill stem, as it is featured prominently in the build of the house and out-buildings. It is a split-level, walk-in basement on a slab which extends to side-walk width outside, with a septic tank.

The Washer (new Maytag Bravos Top Load HE) is on the walk-in wall where the floor is at ground level. The construction of the wall is paneling-studs-cinder block-brick inside to outside. The standpipe abuts the cinder blocks, shares the drain only with a sink on the same wall (junction is below slab) and is not connected to the septic system.

The top of the standpipe is 2" ID PVC (originally 32" high, that I extended to the manufacturers recommended minimum of 39") which (I learned after tearing out the wall) joins a metal pipe approx 1 3/4" ID (probably drill stem; see above)1 foot before passing through the slab, with no clean-out access to be found and no visible gray water discharge outside.

Problem;
With the old washer (it died) we could wash two loads back to back. On the third load it overflowed. Wait a few hours, repeat. Aggravating but manageable.The new washer overflows the pipe during the first drain of the first load.

The manufacturer calls for a drain carry rate of 17 GPM. At an estim. Flow of 4-5 GPM it takes a garden hose 3 min. to fill the standpipe.

So far I have tried chemicals, hot water and compressed air (while blocking adjoining sink drain) with no noticeable improvement.

The metal pipe through the slab and/or the prospect of metal pipe in the ground makes me wonder if snaking is a wasted effort.

Any suggestions regarding how to proceed OR best/easiest/most cost effective options would be greatly appreciated.

8up

I don't have an answer for your question. But, I care that your question gets answered. By my posting a reply now, your question will get moved more towards the top of the list of questions needing answers. Hopefully, someone will come along soon with the expertise to answer your question.