Two washers, one drain

[John Kogel]

Adjoining laundry rooms share the same 2" ABS plastic drain pipe. The pipe connects to a vent stack and a 4" drain.

Is it acceptable for the two washers to share one trap through a Y or T above the trap? That is, can they share the stand pipe?

[Jim Katen]

A clothes washer is equal to 3 fixture units. 

A 2" pipe is good for up to 4 fixture units. 

So, no. 

[John Kogel]

Thanks, Jim. I'm in full agreement, and who can argue with the math? Machines are in separate units with a common laundry room wall, and both draining in unison would be a disaster. A parallel drain pipe is a bit of work but eliminates the Russian roulette aspect.

This made me think of the old Power Miser relay that we used to see here on electric dryer circuits. When one appliance is running, another appliance on that circuit has power cut off.

[Jim Baird]

I once saw a washer draining into a 1 1/4 " cast iron drain.  Owner had found a huge (laundry basket size) funnel that took the rinse load and patiently fed it into the tiny pipe, that also served a sink and its trap.

[John Kogel]

Right, if you have ever seen a standard-sized washer empty into a laundry sink, you know how fast the washer pump will fill that sink to within a few inches of the top.                             

The little sink drain can't catch up, so yes, it needs to be a big reservoir.

Basement laundry drains are fun. I remember one where the washer hose was extended straight up to a very short standpipe/elbow and a drain pipe suspended from the ceiling joists. The sewer drain was in the basement wall several feet above the floor, and the bottom landing for the stairs was there, so up and over was really the only option.

I looked up the specs for the washer pump and it was rated for a max lift of 8 feet, acceptable IMO, but the short standpipe was wrong.