If your going to preach codes you should also mention the need for a cleanout on fixtures connected with a double tee on the vertical portion of the pipe. Using a double wye combo doesn't require a clean out because there is no risk of jumping the fitting and entering the nearby fixture.
When you did your drawings in plumbing school, rosem637, and during your journeyman or masters testing, these details were required so that plans and permits could be filed and isometric drawing could be properly interpreted.
I think that Double Fixture Cross, Double San-T's and Double Wye Combos are the most difficult to understand when and where to use.
some codes would refer to that as s-trapping a toilet, but as stated in the past, toilets do not operate on the same principles as a standard fixture trap.
What if you had a toilet go direct from the flange with a 45, then about 2' of pipe, then directly into the wye hub, so no horizontal arm at all and no 1/8 bend at the wye?
The questions I still have:
1)In the Toto recommended double WYE fitting arrangement, if the center is the only vent, and you had other fixtures also tied into the toilet arm before the WYE, (washing the toilet line), is that vent still a vent for the other fixtures (the tub, lav, washer) or is it now a partial S trap at that WYE requiring a revent somewhere back into the vent above the WYE?
2) If you left it as a Double Sani Tee would it not need reventing with same configuration?
3) Does Toto assume only two toilets are tied into that Double WYE no other fixtures involved?
4) I thought this forum was Love Plumbing University and I could get Continuing Learning Credits on here???