two inline traps at sink???

Just wondering if this is allowed: two sink traps installed one after the other inline (see photo). Any input on this one is appreciated (seems like it would lead to siphonage).

JW Home Inspections, Inc.
Hilton Head, SC

No but somewhat common on older homes.

Do a search for S-Trap. Lots of earlier discussion on this setup.

Thanks Michael
I’ll look up more on the s traps to see if I can find anything more specific. I know it is wrong, just not sure how to describe exactly.

Several “S” trap drain configurations were observed during the course of inspection. In many locations, “S” traps are no longer accepted by the plumbing codes as these traps tend to easily siphon dry even when well-vented. It is recommended that further evaluation be obtained from a qualified plumbing contractor familiar with the local building codes. Repair or replacement should be conducted by a qualified plumbing contractor. The following link provides detailed information about proper drain configurations.

Thanks Scott
great comment and link. The 2 pipes in the photo are actually P traps but used as they are, appear to form one large S trap. Weird and likely amateur.


I find it pretty scarey that an inspector does not know what an S trap is. Gotta make you wonder what else you are missing.

We all started somewhere, and we all have different knowledge levels on different subjects. No one knows everything. And in the big scheme of things, this isn’t a defect that is that huge of a deal.

You had the opportunity to help but chose to try to embarrass a colleague instead. I find that scary.

Hey Bill -

Chill out already…I think John was really asking if it is kosher to install 2 P’s inline with one another to duplicate an S trap.

Agreed - I wasn’t even aware of S-traps before I joined NACHI, but I learned about them (and much more) here.:stuck_out_tongue:

I see this sometimes rather that the cost of fittings to make the turn from a p trap back down towards the floor. People will purchase 2 p traps and connect them together.

Here is todays. This was a re-model done by a very reputable flipper in the area. Excellent work (except for this.)

I inspect in a area where almost every home built in the last 6 years have s traps, i just keep writing them up. One home didn’t even have a vent . no building inspectors in this area