View Full Version : Drake Toilet Back-to-Back Installation Questions:
02-17-2012, 03:13 PM
I’m planning to purchase 2 Toto Drake toilets, either the CST744E (elongated, 1.28 GPF) or CST744S (elongated 1.6 GPF). A few installation questions:
• The toilets will be installed in second floor bathrooms separated by a common wall. The toilet in the one bathroom is perpendicular to the common wall and in the other bathroom parallel to the common wall. Is this a back-to-back installation that I need to deal with?
• The Spec Sheet shows the supply line should be 6” from the center of the flange. Mine is 4½”. And the Spec Sheet shows the supply line coming out from the wall 8” above the floor. My supply line comes up through the floor about ¾” in front of the baseboard, or 1 /14” from the wall. Is this ok?
• I prefer the 1.28 GPF model, but have read about solid waste leaving marks after a flush. Would the 1.6 GPF model possibly leave less marks?
02-17-2012, 06:19 PM
The toilets where the offset is super critical are those that have a skirt. I'm pretty sure you'll be okay with the Drake. The spec sheet shows where it will work the best with still having access and hiding things as much as possible. I'd heed Toto's warning on the spec sheet that shows the proper fitting when using back-to-back toilets. If you don't, you'll have problems...many of the newer design toilets end up with flushing MUCH faster than the older ones, and with the speed they jet the water, it WILL cross over to the one opposite it unless you use the right fitting.
The II version of the Drake uses a different bowl wash than the original and it includes the super smooth glaze which helps things from sticking in the first place.
02-18-2012, 12:14 PM
Any position of the water valve that does not hit the tank or trapway works on the Drake, with the exception of the through the floor supplies.
The back of the bowl can go back pretty far on the floor.
If the supply is on the wall, then 3" or more to the left works.
If you need more rinse, simply hold the handle down a moment. You will save a lot on the water bill, and still have a clean bowl.
I have the Vespin II, Ultramax II, Drake II and the SG Ultramax. They rarely need any cleaning.
02-20-2012, 11:29 AM
RE: Back-to-back installation
I still need to know how a lay person can determine whether one has a back-to-back installation. Possibly the following details will help??
• Two full baths on the second floor separated by a common wall, replacing the toilet in the master bath. A future job is to replace the toilet in the children’s bathroom.
• The master bathroom toilet is removed. All the waste water for both bathrooms merge to a common PVC pipe which 1) exits under the master bathroom toilet, and 2) in the opposite direction of the other bathroom toilet. The master bathroom toilet (what I am replacing) connects to this pipe. Reference the attached picture.
• The merge from all other fixtures in both bathrooms is up stream, i.e. to the right of the section under the toilet in the picture. As you can see, the attachment is angled to send the waste water from this toilet to the left (away from the other bathroom) and down through the plumbing system.
• I don’t know what the piping looks like under the other toilet.
Does this help determine whether I have a back-to-back installation?
RE: Any position of the water valve that does not hit the tank or trapway works on the Drake, with the exception of the through the floor supplies. The back of the bowl can go back pretty far on the floor.
Just clarification. So it sounds like it is simply a clearance issue, correct?
Just to be sure, I plan to go to my local plumbing supply store and make a drawing of the footprint to assure it will not be an issue. This might sound like overkill, but the last think I need to do is order a toilet via the internet and then find it doesn't fit.
02-20-2012, 02:38 PM
If the two toilets connect into the same fitting, then it would be a back-to-back situation. That fitting MUST be of the correct type, or you'll get disruption in one toilet to the other when you flush...pretty much all of the newer toilets flush much faster than older ones and it is this increase in speed that makes the difference. Not to say that that fitting was okay back then, but it worked. Can't tell from the picture...you'd need to look in the wall at the actual fitting. The spec sheet shows what works and what won't.
02-23-2012, 02:41 PM
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.
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?
02-23-2012, 04:33 PM
The back side of (most) any Toto spec sheet shows a picture or what works and what doesn't. A combination Wye works, a sanitary T (cross) doesn't. With older, slower flushing toilets, the waste doesn't have enough velocity to cross over, but the newer ones need to move much faster to get the same job done with less than half the water. Can't see your installation, so, not sure exactly what you have or how it is connected. Wait for one of the pros to see what they think.
02-23-2012, 04:38 PM
I can see it. The pic above is a san tee laying on its back. Its not proper. It'll work tho. That tells me your toilets do not dump into a common sanitary cross.
02-24-2012, 05:42 AM
RE: I can see it. The pic above is a san tee laying on its back. Its not proper. It'll work tho. That tells me your toilets do not dump into a common sanitary cross.
RE: If the two toilets connect into the same fitting, then it would be a back-to-back situation.
Yes, I know toilet 1 is connected to a san tee and I believe toilet 2 probably is connected to a 2nd san tee on the other side of the wall.
And my guess is that there is a 3" section of piping in between these 2 san tee's where the waste water comes in from all the sinks and at least one tub.
So just for clarification on "do not dump into a common sanitary cross" and "two toilets connect into the same fitting". Agree, the san tee's on their back is not proper; the house was built in 1978.
But if I understand what both of you are saying, it is ONLY a back-to-back installation if both toilets connect DIRECTLY to the same (single) fixture. Thus, I do NOT have a back-to-back installation. Correct?
Your response will help clarify this for me and others who might have this problem.
Thanks in advance!
02-26-2012, 11:52 AM
But if I understand what both of you are saying, it is ONLY a back-to-back installation if both toilets connect DIRECTLY to the same (single) fixture.
Thus, I do NOT have a back-to-back installation. Correct?
Your response will help clarify this for me and others who might have this problem.
Can someone respond to this?
I'm not trying to beat a 'dead horse'. It's just that earlier on in this thread it appears that I misinterpreted "If the two toilets connect into the same fitting ...", and spent a few days learning how I might resolve this situation.
But even while showing 2 local plumbing places a picture of what I had, neither said that I did not have a back-to-back installation.
So the clarification is simply to confirm what I now believe.
02-26-2012, 12:13 PM
You do not have what they are considering back to back installation.
02-27-2012, 04:19 AM
Thank you! I will order the Toto's today.