What plumbing traps are illegal by code?

Tuesday, April 14, 2020

Here are six types of plumbing traps that are not approved by the International Residential Code. Here’s the citation: 

1) Building Trap - This is a kind of “whole house trap” that is on the final line out to the sewer. It dates back to the time before individual traps were required for each plumbing fixture, and has been prohibited by the building code for many years. See our blog post What is a building trap? for more details.

2) Bell Trap - This one is essentially a water reservoir cup with a bell shape over it that dips into the cup to form a seal. It is not self-scouring, the seal depth is very shallow, and it is a sluggish drain that clogs easily. Earlier versions of this trap, like the one shown at right, had a curved top seal that more closely resembled a bell.

3) Bottle Trap - These occasionally are included in the box with “designer” sinks when the trap will be visible under the sink. Although not specifically named above, they fall into category #2 of “traps with interior partitions” and are also not self-scouring as required. May be allowed to be installed if corrosion-resistant material under special conditions by local jurisdiction.

4) Drum Trap - Not self-scouring. Often used as a sediment trap to separate out small solids before they enter the drainage system. May be approved to be installed under special conditions by local jurisdiction, such as for a dental clinic, if corrosion resistant material. To learn more, see our blog post What is a drum trap at a plumbing drain?  

5) S-Trap - It’s called an S trap because the shape is a sideways “S.” The trap seal tends to get sucked out when draining because it is unvented. Was once acceptable, but has not been approved for many years. See our blog post What is an S-Trap? for more details.

6) Trap with moving parts - We have not seen one of these mechanical anti-suction devices in a drain in a long time. No picture for this one.

    What’s not illegal? A vented P-trap is always a good choice. Learn more at What is a P-trap?

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

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

Why is there sand in the bottom of my toilet tank?  

What causes a gurgling sound when a bathtub or sink drains? 

Are drop-in toilet bowl cleaner tablets safe? 

What can I add to my septic tank to help it work better?

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

Why is there mold inside my toilet tank?  

What are the pros and cons of a wall-mounted toilet?

Which plumbing fixtures require water shut off valves in a home? 

How can I tell if a house is connected to a septic tank system or sewer?

Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water? 

Why is a backflow preventer required on lawn sprinkler systems? 

How can I locate my septic tank? 

Is a hot water faucet handle required to be on the left? 

Can you live in a house while the plumbing is being replaced? 

Why can't PVC be used for water pipe inside a house? 


What are the common problems to look for when the plumbing has been replaced in a house? 

What's that powdery crust on the pipe connections at the water heater? 

How can I tell what type of plumbing pipe I have? 

What causes low water pressure in a house?

Should I call a plumber or septic tank contractor when my septic tank backs up into the house? 

How do I get rid of the sewer gas smell in my house?  

What are the pipes on my roof? 

Should I wrap the water heater with an insulation blanket? 

My water bill went way up last month. How do I look for a leak?

Why does the water have a rotten-egg smell in some empty houses? 

Where is the septic tank? Are you going to inspect it? 

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

Which water pipes are an insurance problem and possibly uninsurable? 

• Does a home inspector check the plumbing under the floor slab?

• Is it alright to disconnect the washing machine drain from the septic tank and divert it to the ground in the yard?

      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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