Trap question

Is the trap needed at the disposal? Shouldnt a straight pipe be used.

If there is a issue can someone explain or is this OK.

A trap at the disposal is fine.

Thanks Dave

Except that unless I’m looking at it wrong, you shouldn’t have two traps in succession on the same drain line.


They could have done it this way also…

They are on the same line. What would the problem be with the extra trap?

In this case, probably nothing because the second sink drain acts as a vent in-between the traps. Two traps in the line though can act as an S-trap, or can cause poor drainage.

In any case, it looks amateurish, which should raise red flags! :wink:

That is a double trap, plain and simple. A tail-piece cannot be used as a vent, and a trap is not allowed to drain to another trap (with few exceptions).

It’s wrong and should be corrected.

If this is a Insinkerator Badger model, that is the way they recommend you install it.
In their installation instructions it says ( if you have a double sink, use separate traps for both sides) That is how i installed mine and have had know problems. It has a 3 yr. warranty, so i put it in the way they wanted it.

That is not the proper way to install the traps - period. Even if the manufacturer says “trap each sink separately,” this is not the way to do it.

In areas where the IRC is used, a shared trap arm is allowed, but the traps are required to be at the same elevation and attached to the trap arm with a Wye or directional fitting, such as a back-to-back.

In areas where the UPC is used, you cannot have a shared trap arm and must use a common trap (a single trap) regardless of the manufacturers recommendations.

Where’s the vent for your sink Christopher?

Double-traps, as illustrated in the photo, is a plumbing code violation, and illegal, under the IRC/IPC plumbing regulations.

Double trapping can break the trap seal and allow sewer gas to enter a house.

Besides that, the trap for the garbage disposal is installed BACKWARDS <rolls eyes> and needs to be removed.

Yea, that too :wink:

The second sink drain would only act as a ‘vent’ if the sink is not filled with water. If it is filled with water, then one or both traps could siphon breaking the trap seal and allowing potentially harmful sewer gases into the structure.

This is an illegal installation and needs to be corrected.

Double-trapping as illustrated here is a code violation under most all plumbing codes.

How about this type of installation?

IMO, a lot of the confusion is the result of the InSinkErator instructions, specifically step 11.4 :

“If you have a double sink, use separate drain traps for both sides.”


There is nothing wrong with that arrangement, provided that both traps are properly vented

That isn’t double trapped even though there is only one outlet for two traps.
“Double trapped” is when they’re in series, IE the water leaving the first trap enters the inlet of the second trap.
Actually that situation is technically two “S” traps since they’re not properly vented.

Where are you getting double trapped from? Serious

That is not a double-trap situation since the traps are not in a series.

The picture in post 1 is a double trap - two traps in series.

The picture in post 9 is not a double trap, but it’s still improper.