I would like to add a diverter valve to my washer's drain line to facilitate a graywater system. I'm thinking of shortening the washer drain so I can relocate the P-trap higher up and add the diverter valve beneath it on the main stack. If I were to do this, what's the shortest that I could make the washer drain? What does the code say, and what does sanity say? If necessary, I can just move the washer box higher up; it's a little low as it is. Here's a picture to show my thoughts:
The dryer ducting is all going to be removed, and the 220v outlet is going to be relocated, so ignore those. And needless to say, that cast iron is going to be replaced with ABS.
Best Answer
Practically speaking, what you want to do is fine. The minimum horizontal slope is 1/4 inch per foot and the max is 3 inches per foot unless vertical. the inlet of the washer drain must be above the height of the washer. This is usually 36 to 38 inches minimum for floor seated washers. Obviously, if your washer is set on a platform, you will need to adjust the height of the drain inlet to be above the washer. I like to see at least a foot to 18 inches higher than the washer so that the drain can keep up with the washer pump and not overflow. I caution you however, if the diverter valve slows the drain flow at the current drain diameter, you may need to increase the pipe/valve diameter size to avoid back-up and overflow.