I found this message on this forum https://www.askmehelpdesk.com/showthread.php?t=4331&highlight=RUNNING+SHOWER+TRAP

I have the same issue I need to trap a 2nd floor shower (floor joists 2x8) so I want to know if I can do this thing called the running "U" trap and how I build one. I want to run 2 feet of pipe so I can get out from under the shower and then do the trap there. Do I just make the trap out of 90 degree elbows? Does the pipe entering the trap have to be higher than the pipe exiting the trap? Or the same and the pipe just needs to be sloped at 1/8" per foot. Thanks for your help.

Scott

Hi Scott,

For a running trap you'll come off the shower drain with a 2" DWV elbo and arm out the 2 feet you need into a DWV stree elbo. From there attach a 2" return bend with another street ell and you have your running trap