Size of drainpipe for washer and water softener

[Theodore]

Hi,
My washer discharges to a 42" high 1.5" diameter vertical drain pipe. There's a P trap at the bottom of this pipe, and then the drain runs horizontally (1/4" drop per foot) for about 5ft and then discharges to a 4" diameter pipe that goes through the basement wall and to a drywell outside.

I want to also send my 3/4" dia watersoftener drain to this same 1.5" diameter vertical drain pipe. I plan to have an air gap by adding a wye (see sketch).

1. is my air gap solution acceptable?
2. is this all too much flow for a 1.5" pipe? I can't find any references for what's allowable/acceptable.

Thanks for your advice.
Regards,
Theodore

 

[Cacher_Chick]

The current code for a washing machine calls for a 2" drain, but there are still a lot of grandfathered 1-1/2" installations in place.

Given the slim chance that your washer would be running while the softener was regenerating, you could leave it as is. If you feel like rebuilding it, do it in 2".