After consulting with a professional plumber, I assembled a drain array for an upstairs toilet, shower, and sink. The structural realities of the situation required me to elbow the 3″ toilet drain from horizontal to vertical, bring it down 14 inches to get downstream of the shower and sink drains, then long-sweep it into the stack. The center of the toilet flange was exactly 17 inches from the center of the stack.
The inspector begged to differ, however, insisting that since the drain pipe travels that short vertical distance–as opposed to having a continuous air gap above the grade of the horizontal drain pipe and continuing at grade into the stack–it was a separate branch and required a separate 2″ vent to rejoin the stack six inches above the flood level of the toilet fixture.
Because of the structural situation, he’s going to allow me a few inches of horizontal travel in the vent pipe so I can bring the vent pup up an outside wall–rather than tearing into the sill plate and through an intervening stud–as long as I provide a clean-out in the vertical 2″ vent pipe.
Before I do that, I’m wondering if it’s permissible to fabricate a vent fitting. With a 2 3/8″ hole saw and some solvent cement, I’ve joined a section of of 2″ ABS to a section of 4″ as an experiment. The joint is absolutely air tight, and so strong I can’t twist it apart with a pipe wrench.
If I could do this at the top of the 3″ elbow that turns the toilet drain pipe to the vertical, I could satisfy the “no horizontal” requirement without cutting apart all my glued fittings to replace that offending elbow with a new manufactured fitting.
Legal?
I’m also wondering what incredible pressure-differential event could occur that would make my original arrangement suck out the toilet’s p-trap and expose us all to escaping sewer gas, if anyone has the inclination to explain.
Replies
Your pro plumber gave you a proper solution; there is no need for additional venting. The shower & sink are properly vented and would not create a pressure differential at the toilet trap. I would ask the building code official to produce the code language that supports his request.......
Actually, I did request the language, and got the attached PDF of Page 84, 2017 Oregon Plumbing Specialty Code with highlighted sections. I believe the rationale is in the first sentence of 905.2 Horizontal Drainage Pipe, according to which the invert of a vent pipe must take off above the centerline of the drain pipe. He's saying the vertical section violates that requirement, I guess--though I thought toilets, by virtue of automatically and gradually refilling their p-traps after the (possible) suction event of a flushing, were excused some of the requirements about an air gap clearing the weir of the p-trap. I'll also include a photo of the original installation.
Again, the center of the toilet flange is 17" from the center of the stack. The top tee, oriented away from the viewer, drains the shower at a quarter-inch-a-foot grade 42" from the outlet of its p-trap and 51" from the center of the drain flange. The next tee down drains the sink, with an AAV 8" above the trap arm in the sink cabinet--I was concerned about the little step-down into the stack for this branch, but the inspector had no issue with that.
Bear in mind we're doing all this by photograph via email, due to COVID-19 concerns, and that I've no interest in getting the inspector irritated unless my objections are rock solid.
Still would very much like to know if fabricating my own ABS connector to fit the situation would be kosher...