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What is the maximum number of slip joints allowed by code under a sink?
Saturday, October 24, 2020
Slip joints “shall only be installed on the trap outlet, trap inlet and within the trap seal,” according to the International Plumbing Code (IPC 405.8) and the Florida Plumbing Code. That means only a maximum of three slip joints are allowed. We regularly see installations that have been approved by the local building department with more than three, but the additional slip joints are before the trap, as in the photo above of the waste arm connection from the disposal to tailpiece. So it is not strictly enforced.
But excessive use of slip joints after the trap is one indication of an amateur plumbing installation done by a homeowner or handyman. The photo above shows an attempt to replace an existing sink with one that's a different size. Four additional slip joints were added after the trap, instead of a direct connection, to extend it, along with an unrated accordion-type pipe as a final elbow.
There are multiple problems here: the long trap arm sags in the middle, and the accordion-type pipe turns uphill at the end. This makes the whole trap arm into a large extension of the sink trap, with standing water all the time and debris buildup in the ridges of the accordion pipe elbow. So you end up with a sluggish drain that clogs easily. Also, a dishwasher drain hose should be connected before the trap to avoid sewer gas leakage, but was connected after it.
Also see our blog post Can a slip joint pipe connection be concealed in a wall?
•••Thanks to James Freeman, of J.W. Freeman Plumbing, for help with this article.•••
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