S-TRAP Verification

I called this up as an S-trap the other day but the plumber called in to fix it is saying I am wrong. Before I get into an argument I thought I would put up a picture to see what the guru’s from the message baord had to say. Yes I did notice the drain for the dishwasher.:mrgreen:

Spidell 054.jpg

Spidell 054.jpg

Spidell 055.jpg

Spidell 053.jpg

Sure looks like an s-trap to me, but I’m not a plumber. Why argue with him? He’s the professional plumber, have him put it in writing that it’s not an s-trap and it’s fine as it is.

Looks like an S-Trap from here, but would need exact measurements to verify or dispute the claim.

Example of measurement to convert S-trap to P-Trap…


I guess I forgot to put in the original post that they want me to pay the bill. It is the p-trap going into another 90 and then about 3 1/2" to the waste pipe.

Greg, in my posted diagram, (Ex 2) the measurement (2x trap dia) is the key.

IMO… the reason the plumber is not calling this an S-trap is due to him using (Ex 3) for that measurement, when in actuality, it is still (Ex 1). The 45 degree angle down-slope is NOT to be misconstrued as horizontal, and MUST be considered as verticle.

SO… if the measurement (EX 2) is 2x the trap diameter or larger, it is NOT an S-Trap. If it is smaller than 2x the trap diameter, it IS an S-Trap.


Hope that’s not too confusing.


Not at all. I have looked over the pics and the examples and I do beleive I am correct. I just sent him the diagram and an explanation so we will see what happens! Thanks Jeffery

I wouldn’t consider it to be an “S” trap just because the trap arm is connected into a wye rather than a sanitary tee.
The difference between it and the two “S” traps in the laundry stand pipe demo pictures is this one has a continuous vent.

The dishwasher discharge however needs to be trapped to prevent sewer gas from entering the dishwasher unless the dishwasher has a positive closing drain valve.

Fyi… The short arm leading into a verticle drop is what creates the S-Trap. Any drop from horizontal is considered verticle.

The reason that “s” traps are non code compliant is because they can siphon dry and allow sewer gas to enter the building.

This trap will never cause a problem since it has a continuous vent.

That information is not shown in the OP pics or statement. How did you arrive at that conclusion?

good call on dw

Here is the answer from a Master Plumber in my area to the question is this an S-trap:

I forgot to come back on with an update. Sorry guys. Ok first and foremost the seller admited that a local handyman with no credentials dig the work and so wheen they called him back to fix it he was ticked off and would not agree with me. A plumber from town got called in and fixed it. I talked to him a couple of days later and he confirmed it as an S-trap. He also talked about the 42" rule for the turn. The dishwasher drain was also wrong which we knew about. I win I win I win. Just not what it was i won!!!

Awesome Greg! Those confirmations are so rewarding especially when some hack is the one disagreeing and posing as the “expert”.