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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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Here’s links to a collection of our other blog posts about PLUMBING PIPES:

How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

Can galvanized steel pipe still be used for new water lines in a house? 

How can I tell if I have cast iron pipes in my house? 

What is the difference between green and white sewer drain pipes?

Is a washing machine drain hose required to be secured at the standpipe?

What are the abandoned pipes sticking out of the wall in my house?  

What are the code requirements for plumbing vent terminations?

What are the code requirements for layout of drain piping under sinks?

What does polybutylene pipe look like? Why is it a problem? 

• Which water pipes are an insurance problem and possibly uninsurable?

• Can you connect CPVC pipe directly to a gas water heater?  

     Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

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