Wall hung toilets - does anyone actually know how to plumb them?

[Gordan]

I get that these are sort of a specialty item, at least in the residential market. But come on. Even Toto technical support could not provide information about the plumbing requirements for the CT-418FG. The guy was saying, "well, every picture I've seen has the outlet discharging straight down." Thanks, buddy. Except one can find some pictures of European origin which have it discharging horizontally (with the minimum drop, of course.) And some of these even suggest that the fixture should discharge into a santee and not a wye, in order to allow venting. And Geberit says that the pipe can be angled to 45 degrees from vertical. So, plenty of inconsistent information. Noone seems to understand why they're saying what they're saying, or if they do, they're hiding it pretty well or just don't want to share.

Here are some simple questions:

1) Does the outlet elbow have an integral function in ensuring flushing effectiveness (basically, completing the S-trap and thereby enhancing siphoning) or does it merely connect the outlet to the drain? If it's merely connecting, then a horizontal drain should suffice as with any other fixture, the bottom of the rear outlet is the weir of the trap, and one should be able to locate a vent at any point past 2x drain diameter away from the outlet. Correct?

2) If the outlet elbow DOES have an integral function in ensuring flushing effectiveness, what's the minimum drop from the bottom of the rear outlet that would allow it to perform this function? In other words, how much vertical drop before one may turn horizontal (and vent)? Below the bottom of the bowl?

I've seen repeated queries on this forum about the requirements for these toilets and no substantive reply. Please - considering the reputation of this site, it should not be difficult to get some base-level understanding of these devices. Codes are silent; as far as they're concerned every water closet discharges into a flange on the floor which is connected to a closet bend, which is obviously bunk. If you're in the position to educate the masses, including the originator of this thread, your knowledge sharing will be greatly appreciated.

Thanks in advance!

[DougB]

I'm a DIy'er and planning to install one of these later this summer.

If you go to the Toto web site http://www.totousa.com/ProductDetail.aspx?ProductId=729

They have the engineering drawings and installation pdf's.

It states: For vertical drain installation, drill a 3-3/4” hole on the subfloor 3-1/2” from the front of studs.
For left or right drain connection, it is recommended to install the drain at 45º or more from the outlet horizontal.

[hj]

A "blowout" bowl would be the ONLY one that would benefit from the 'siphonic action" of a turned down elbow, and they are NEVER used in residences and few commercial installations, except prisons. Once the waste gets "to the wall" it can go in any direction you need to in order to get the pipes installed. ANY "competent" plumber can install these. It is when engineers get involved that it becomes difficult.

[Gordan]

Thank you, Doug! It figures that Toto would put this information in their owner's manual rather than in their installation manual. Thank you for pointing me in the right direction!

And thank you, HJ, for providing the big picture. It's most helpful!