I have a vexing problem regarding a kitchen sink... it will be moved to another location during an extensive kitchen remodel. There is a bank of windows only six inches above the flood rim... which creates the problem of just how to vent it. I've thought of two options and I need your feedback.

Option 1:

When the waste water enters the wall it doesn't drop down... instead, it makes a 90 degree turn and travels (sloped) horizontally through the cripple studs. It will travel approximately 5 feet until it emerges through the other side of the double king stud... and then it drops down where water drains... and the vent rises vertically and will eventually re-connect with an existing vent.

Option 2:

When the waste water enters the wall it drops straight down. The vent angles off at a 45 degree angle. The vent travels through the cripples at a 45 angle until it levels off (sloped properly but basically horizontal) somewhere near the underside of the sub-sill. It emerges through the double king stud and then it is free to travel vertically.

I like option 2 because I think it will be less prone to clogging. But I don't know if a vent can travel like that, especially under the flood rim. Also, is there a rule (I remember this but I could be completely wrong) that a vent can't make a vertical rise after a horizontal run if it is still under the flood rim. But a vent can travel in a combination of sloped horizontal and 45 degree rise while still under the flood rim... when the 45 takes it 6 inches above the flood rim, then you're free to rise vertically.

Am I correct or completely off base? Something tells me I could use a little education here.

Other questions:

Can a kitchen sink (also a dishwasher) be vented with a 1 1/2 vent? Or does it have to be a 2 inch?

There is an opportunity to create a clean out... Is it ill advised to put a clean out that opens in the under sink space? Or should it be opened from outside the house?

Thanks, Tom... Again, I hope you don't mind me contacting you like this.

Best,

Paul Myers

Hi Paul, Welcome back!

Sorry, but I don't care for either option #1 or 2. Both 1 & 2 are "S" traps and that's a definite no-no.
I would go for number 1 if you went into the wall and 90'ed over five feet to a existing vent stack. This is the way most kitchen sinks are configured.

" Can a kitchen sink (also a dishwasher) be vented with a 1 1/2 vent? Or does it have to be a 2 inch?"
Our code allows for 1 1/2" vents but our inspectors like to see them at two inches. Check your local code. Regards, Tom

Hi Tom,

Thank you. Concerning the 'S' trap possibility... If the horizontal pipe (trap arm, I believe) just downstream of the P trap... the pipe that actually enters the wall... if that pipe is twice as long as its diameter, isn't that the minimum length it would take to prevent an "S' trap situation?

Thanks again!

Paul Myers

If you're asking if you can build a "S" trap but get it passed because the stub out pipe is twice as long as its diameter the answer is no. A "S" trap is a "S" trap no matter the pipe size. The limit to a 2" drain line is 5 foot from trap to vent. Regards, Tom