Update - a bit long, but I wanted to add the details
RE: Water supply line relative to new toilet footprint
I went to my local Toto dealer and made a footprint of the Toto Drake to see if the water line coming up 6 ¾” through the new tile floor was going to be a problem. The water line is ~2 ½” on a diagonal from the rear left of the footprint. So there is no clearance issue with the footprint, and there should be no clearance issue with the tank (14 5/8” above the floor) and the trap. So I believe this issue is resolved.
RE: - If the two toilets connect into the same fitting, then it would be a back-to-back
So back-to-back it is. Arg! Reference my attached drawing. What I know:
• The Toilet 1 (T1) closet flange is attached to a 3” sanitary tee lying on its back.
• All tub, sink and Toilet 2 waste water flows through the wet wall separating the rooms and under T1 and toward the front of the house. It then exits through a pipe that runs to the basement.
• There is a 1 ½” vent for the sinks that goes up through the attic and out the roof.
• There is a 3” vent for the toilets (and tubs?) that vents the same way.
• The 1 ½” vent line connects into the 3” vent line in the attic.
• The flange centers for toilets 1 and 2 are approximately 33 ½” apart.
• My guess is that Toilet 2 is probably also connected to a 3” sanitary tee.
Between the little I could find on the internet (surprisingly not much), and conversations with a few plumbing establishments, there appear to be 3 alternatives (# 1, 3 and 4 below) in order of complexity:
1. Do nothing. That is, install the toilets and then see if there is a problem. If yes, then deal with it then.
2. Replace each toilet sanitary tee fitting with a 45 degree wye, a 45 degree street elbow and a closet flange. BUT, I don’t think there is sufficient vertical space in the joist bay for all of this. The joists are probably 2” x 9”, the same as in the basement. The wye with a 45 takes up ~11 ½” even without a street flange.
3. Same as # 2 except lay the wye on its side. This may work if the 3” waste pipe from toilet 1 runs close to one of the joists.
4. Same as # 2 except lay the wye on its side. AND if it does not fit the bay because the 3” waste pipe is centered in the joist bay, then sister a joist to one of the joists so that the existing joist can be cut out for placement of the wye on its side.
As noted, I believe alternative 2 is a non-starter. Alternatives 3 and 4 would require my opening up the ceiling in the living room beneath the bathrooms. This same section of ceiling has to be replaced anyway since one or more bathroom appliances leaked in the past and stained part of the ceiling.
My plan is to install a Toto Drake and try alternative # 1. If when I flush one toilet, all I have is a little bit of gurgling, or a slight rise and fall in the bowl water level in the other toilet, then I can probably live with it. And I may not even notice a problem initially with the old 3.5 GPF for toilet 2 still in use.
However, once both toilets are replaced, if flushing one toilet drains all the water from the other bowl, and possibly the trap, then I will move on to alternative 3, if doable, or alternative 4.
Questions:
1. On another thread, Terry stated: “Any toilet with a 3" or larger flush valve will push some water from the opposing toilet bowl. Using a slower flushing 2" flush valve will mitigate the issue. That being said, I do plenty of installs on back to back toilets, and yes you can lose some water in the opposing bowl. It's not that big a deal.”
Given my 3” vent and the 33 ½” between the center of the 2 flanges,
in your opinion, what is the likelihood that I will not have a problem?
2. Assuming alternative # 1 doesn’t work, are there any other alternatives than 3 and 4 listed above? Opening up the newly tiled floor is not an alternative.
3. Is there anything else I need to consider on this back-to-back issue?
thanks
