Back to back toilets

newbie here, so likely an elementary question, however would certainly value any input or advice.

We have lived in our home for 1 year (bought it new), and we have back/back bathrooms downstairs - one bathroom is 1/2 bath with toilet/sink - other is toilet only which hangs off master bath.

Issue we have is when we flush the toilet off our master bath (which lines up directly behind the other), the 1/2 bath toilet splashes water out of it with a few big bubbles that come up. Both toilets are standard 1.6 gpf (one is a briggs and one is an eljer if it matters).

Only other info is before we figured out the other toilet was bubbling, we had slightly detected a sewer gas type odor somewhere in the vicinity of the bathrooms- we had spent a few months troubleshooting this by changing wax rings / doubling up wax rings, etc. but did not help.

However, now that we luckily saw the bubbling firsthand, I would assume we have either some type of blockage? or venting issue? or issue with how the 2 toilets share a vent pipe? does it matter the toilets are different brands?

back to back

What you have described sounds like a clogged drain,if the problem began day one that you moved in then there may be some merit to a problem with the distance of the closet bends to the vent serving the sanitary cross.

thanks - is there a max limitation from the cross to outside vent?

is there a max limitation from the cross to outside vent (that is if I understood your question correctly)? thanks in advance.

Yes,from the outlet of the toilet,or the closet bend,the pipe is to be at least 18"in length to the connection at the cross,(double sanitary tee)

update - had plumber come out - need Feedback pls.

ok, finally had the original plumbing co. come out that worked with our builders in the original construction - good folks, but wanted to pass along their "diagnosis" for feedback here in the forum:

basically, it seems that my back/back toilets are very close - apparently there is no code here in Dallas TX about length to cross - under the slab there is a cross that both feed into on each side - sides of cross meet in the middle, down is the drain / up is the vent - based on the 2 toilets I have, the Eljer obviously produces a larger flush (than the builder grade Briggs); thus, shoots across the cross and bubbles out the other end. When Briggs flushes, it simply a "ripple" and does not bubble on the eljer side. (***note, they ran a snake and camera to the wash out and street - zero blockages)

plumbers suggest as 1st OPTION: cutting a 18" by 18" hole in the slab, and raising one connection (above current spot on cross) and then blocking off the original spot - result, cross is gone, and no longer will shoot across.

plumbers suggest as 2nd OPTION: going back to lower grade flush since apparently the current plumbing (while obviously flawed) is still operational and working.

Would very much appreciate thoughts here - this is luckily NOT AT MY EXPENSE and would be covered by warranty - the slab option is intrusive but could fix things?? or would be best to get 2 lower grade toilets?

Lastly, are these guys missing anything? They ruled out venting immediately - why so fast? They didn't even look to confirm venting is ok? Per my original post, none of this really explains the hint of sewer gas that we have detected off/on since moving in....

thanks so much...regards.

Double fixture fitting

Not a pro, but I am installing back to back toilets. Our code requires a "double fixture fitting" and doesn't allow a double sanitary tee for this application. The difference is the two drains meet further down the fitting. Could be that replacing the cross with a DFF might solve the problem?

Hazel

The lower grade toilet would be the least intrusive+most cost effective for the warranty backer,but you could never have a pressure assisted W/C in the future if you decided to change,there is discussion going on to make toilets 1.3gpf,stacking the san.tees would solve the problem,that is why the IPC addressed the double san.tee with a developed distance of 18"closet bend to the fitting of the san.tee,that piping arrangement would never fit in a 2x6 wall and rough in at 12". A double wye w/an eighth bend horizontially with the vent just downstream of the double wye would be one way to do it.

thanks much for the reply

thanks for insightful reply and post.

we've decided to go the "intrusive" route and let the original plumbers go in and replace/correct the current configuration. we figured we could put up with a temporary mess to do it right (and no cost to us)

last question: can I assume our intermittent sewer gas issue could also be solved with the fix? assuming the source of the sewer gas is being caused by the pressure created by the current design (i.e. afer each flush, sewer odor is being forced back into the bowl/room due to the pressure created); we have noticed it's worse after flushing (since we have flushed so much lately testing this issue out) - thanks in advance.

Smart choice. Chances are that at some point in the future, you would have regretted going the other way. Especially, since it is still under warranty.
Speaking of warranty, make sure you keep a file of all these documents and don't let your warranty expire without you being (speaking of the sewer gas smell) completely satisfied.

sewer odor

last question: can I assume our intermittent sewer gas issue could also be solved with the fix? assuming the source of the sewer gas is being caused by the pressure created by the current design (i.e. afer each flush, sewer odor is being forced back into the bowl/room due to the pressure created); we have noticed it's worse after flushing (since we have flushed so much lately testing this issue out) - thanks in advance.

it seems very obvious that with the issues we're experiencing, the sewer gas piece must be tied in somehow - but just don't want to make any assumptions...so just was curious if my theory above is correct?

*plumbers come tomorrow to start the work - guess we'll see if it corrects everything - should I even question the venting?