Phil_H
Wallingford: I am curious what plumbing code you follow. The 2000 Uniform Plumbing Code requires a 2″ drain for a clothes washer standpipe.
Rocketman: 1-1/2 might work but . . . I would recommend that you get local expert advice. There is more to drainage systems than sizing pipe and having pipes point down-hill.
FYI: some codes (UPC for one) will allow a smaller (1-1/2″) trap on a laundry sink with the washer discharging into the sink.
Phil H
