Drum trap pipe size

Questions, answers and advice for people who own or work on houses built during the 20th century.

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Posts: 1
Joined: Tue Jul 27, 2021 11:20 pm

Drum trap pipe size

Post by grb »

Hello all,

First time homeowner of a 1937 home. I noticed the shower drain was slow, so I got into the access panel behind to find a drum trap. Opened it up and noticed the trap had a different size united inlet and outlet. The inlet looks to be 1 1/2" cast iron and the outlet appears to be much smaller, maybe an inch or so. The water gets backed up there. I've snaked all the way to the stack. The sides of the outlet are clean so it doesn't appear to be buildup. No issues with the sink or toilet (both of which are between the stack and tub). Is this a normal occurrence in older homes? Never seen anything like it but I've only ever worked on newer construction.

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Joined: Sun Oct 10, 2021 10:23 pm

Re: Drum trap pipe size

Post by Timplex »

If the outlet pipe is smaller, there should be a reducer bushing screwed into the drum trap.
The way drains work, is the pipes get bigger as they flow downstream, not smaller and this prevents serious clogs.
Why someone would use a pipe that small in a drain is beyond me. Maybe the old one rusted and was replaced by something laying around?
Try to repair it back to the way it is supposed to be.
Or else, what many do, is just install a normal p-trap, those drums are more problem than they are worth.

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