Thread: Double trapping at kitchen sink

Is this considered double trapping and is it allowed? Thanks

Originally Posted by mark petty

Is this considered double trapping and is it allowed? Thanks

Yes, No

Swivel the first trap 90% so it is horizontal.

Originally Posted by John Kogel

Swivel the first trap 90% so it is horizontal.

John, Rick
Thanks for your quick replies.

A garbage disposal should have its own trap (which it has) but it should be connected to the drain downstream of the sink trap.

Originally Posted by mark petty

Is this considered double trapping and is it allowed? Thanks

Amateur work - Doesn't understand the purpose of the trap is to stop sewer gas, not catch things that fall through the drain. The lower one is all that is needed. The dishwasher is usually plumbed into the disposal - that's the purpose of the nipple above the drain on the disposal. Although it has a redundant trap (double -trapped) - This system looks safe and workable.

Originally Posted by Tabb Jensen

Amateur work - Doesn't understand the purpose of the trap is to stop sewer gas, not catch things that fall through the drain. The lower one is all that is needed. The dishwasher is usually plumbed into the disposal - that's the purpose of the nipple above the drain on the disposal. Although it has a redundant trap (double -trapped) - This system looks safe and workable.

The trap at the disposal is reversed left to right as we look at it. This means that the disposal will hold water in it (centrifugal force is sending it through the trap when the disposal is used, but water will fill the disposal before one runs it). This is an incorrect installation and not considered correct. If it was below just a sink it would function but hold more water than desired or needed and could leak more easily.

As the trap is used to stop sewer gases only one trap is necessary technically. The disposal can run to the sink down pipe and then to a single trap. This means that a "divided end outlet T" is used in the assembly. If the disposal becomes old and does not chop to a small enough particle size or hair (corn silk) passes through it may clog the divided T. Without a divided T the water could easily pass from sink to sink, but the sewer gasses are still blocked.

Replacement with a proper functioning disposal is advised in that condition. OR one could install two P traps. The preferred method for two traps is to place a Wye at the wall and then run two separate drain systems to the Wye instead of a trap to the down leg of the sink and then another trap below.

Except for the reversed condition of the disposal's trap at the disposal causing back up into the disposal everything should be ok, just not as "preferred".