As I stated above, the hose extension required will not fit in the plug, not even close, diameter of the rubber piece is more than 1/4" bigger than the plastic hose that would normal go into the plug. Using the supplied plug is out. So not sure how another standpipe would help.My water softness varies depending on if the softener just ran or is close to needing a recharge.
I had the same problem of an A/C condensate drain shared with the washer. I moved the A/C drain elsewhere to another drain pipe and used the plug. Only problem I have had since is the hose coming up out of the drain pipe some from vibration and foaming over again so I had to secure it to stay in place.
As mentioned a dedicated washer drain pipe with a trap added would solve it. Myself I would T the existing standpipe, add a trap, and washer drain pipe. Yes the washer would go through two drain traps on the way out. Get a quote as it should be cheap enough to just do it.
I wouldn't need a quote, PVC is an easy DIY job. But as stated, there is no space left between any couplings, so if I cut it, there will be no pipe to attach anything to. How do you tee an existing drain pipe? Double traps are against code as well, can cause an airlock, and overflowing. I do appreciate the suggestions, just don't see how it can be done. Maybe a picture?
The good news is, it hasn't done it again in the seven weeks since I posted this, about 18 loads.