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What is a double trap in plumbing?
Monday, March 30, 2020
A double trap is two plumbing traps in tandem, one after the other in line, and this often causes the first trap to get sucked out by the last trap. An example of one sink trap connected to another sink’s trap is shown above. Only one trap is allowed between a plumbing fixture and a trap arm by the International Residential Code (IRC P3201.6). The right sink should not have a trap.
Double-trapping the same sink, like in the two examples below, is also not allowed—although we once listened to a passionate argument by a homeowner that it’s actually twice as good. Oh well. It creates an excessively large trap volume and makes the drain more likely to clog.
Also, see our blog posts Why is it a problem when a trap under a sink is installed backwards? and What are the code requirements for layout of drain piping under sinks? and Can I make a trap under the sink from straight pipe and 90º elbows and Why is there a flexible accordion pipe under the bathroom sink? and What is an "S-Trap" under my sink? Why is it a problem? and What is a P-trap?
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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?
• Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection?
• 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 causes a gurgling sound when a bathtub or sink drains?
• What is a "combination waste and vent" in a plumbing system?
• What is a galvanized nipple?
• What are the pipes sticking out near my water valves?
• How do you accurately find a broken water pipe leak under the floor slab?
• What is the difference between water pipe and sewage (waste) pipe?
• Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water?
• Is a hot water faucet handle required to be on the left?
• What's that powdery crust on the pipe connections at the water heater?
• How can I tell what type of plumbing pipe I have?
• Why is there a flexible accordion pipe under the sink?
• What is the difference between PVC and ABS plumbing pipe?
• What is the difference between water service pipe and water supply pipe?
• What are the pipes on my roof?
• Why is old galvanized steel water pipe a problem for homebuyers?
• 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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