View Full Version : Toilet drain replacement

10-05-2009, 09:04 AM

The current toilet drain had a 4" hole bored into an 8" joist - needless to say, the joist was very bouncy and I'd always wondered when I would come crashing into the kitchen on the toilet. I've replaced the joist and I'm looking for an alternative to routing the toilet drain. Straight line to the stack (the stack is the top circle in the pics), is about 3.5 feet. There was no vent in the past.

1) Run the drain along the same line as the old, but have it drop below the ceiling. Tee into the stack, no vent required. This option requires me to create a bulkhead that protrudes into the middle of the kitchen, which I'd like to avoid.

2) Can I do what I tried to show in the picture below? Can I run the drain in the joist space until almost the wall, put a 90 on it, and wye into the stack? The wye and 90 would be hidden in the bulkhead above the cabinets. Can this be done without a vent? There would be a sharp drop (from the wye), just before the toilet drain enters the stack.

10-05-2009, 11:14 AM
I don't think I explained myself well enough. My option 2 would not require any holes bored in the 2x8's. I realize that making a hole for a 3" pipe is not feasible.

When I said a 90 and a wye, the 90 would be at an angle attaching to the wye from the stack - or a small extension off the wye. I tried to draw the side view from the main floor here. Does this make more sense?

The wye would be hidden in the bulkhead above the cabinets and would not require any cutting of the joists. Where the blue is, that's the horizontal drain line up in the joist space from the toilet (I can hardly use Paint, let alone draw in 3D). I just don't know if I can have a drop like that without a vent.


10-05-2009, 11:50 AM
I remembered I had these Ikea sketchups. I tried to add in the drain, but hey, 3D is not easy!

The dark blue is my see through 3D of the vertical stack. Othewise the horizontal pipe just blocks everything out.


The below is similar to the first paint sketch I did, but just in 3D.

10-05-2009, 11:59 PM
Does the three inch continue up through the roof? Was that the existing vent? You have the right idea with wye/90, but instead of the 90 use a 3x2 low heel outlet and use the 2" to vent. You can run the 2" up in the wall above and tie it into the 3" once it's 6" above the toilet.

10-06-2009, 05:24 AM
Your description was adequate without the drawing. A toilet is the only fixture that would work with your design, and only a very fussy inspector, with a lack of knowledge about the hydraulics involved, would reject it.

10-06-2009, 07:12 AM
Thanks for the replies guys, but now I'm really confused. hj says no vent required, and dcelite says to add one in - I'd rather do no vent, because it's easier, but which is correct?

10-07-2009, 12:18 AM
I agree with HJ. The system will work fine in your plan. However, I would do it with the vent off the san tee (in place of your 90) just because we do have too many "picky" inspectors out here.

10-07-2009, 07:00 AM
A toilet, by design, has an "S" trap inside it. An "S" trap works BEST without a vent, (actually it ONLY works without a vent). So, your drawing, without an additional vent, would mean the toilet would flush even better than originally since it its vent is after the turn down which extends the "S" trap's effective length.