Toilet siphoning when 2nd toilet is flushed-PIC

antinusk

The toilet on the left has a problem with the water level dropping about 1/2" whenever we flush the toilet on the right.
I'm thinking that the water must be rushing over the Y fitting on the left and sucks just enough to take a little water from the bowl. If we keep flushing, eventually it sucks enough water out to let the gas in.
Am I going to have to cut all this out?
The stack pipe that you see does have another (tub)drain connected to it but that doesn't seem to affect the toilets at all.
I had an expert plumber come over- he didn't think there was a problem since it wasn't clogged. I really want to fix this though.
Thanks

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Pirulo

It seems to me that the central stack pipe is blocked and is not venting the toilet on the left. Being it horizontal for a while, check if it is not obstructed with leafs coming from the roof (I have seen that many times, even 4" pipes).

If the problem is still not fixed, then you'll have to cut pipes, try connecting the horizontal run coming from both toilet (efectively creating a loop for air movement). An AA valve on the left pipe can help too (attached on the 45 degrees descending part, and going up over the level of the toilet rim (or risk a messy accident if ever there is an obstruction on the pipe).

allthumbsdiy

just a side question. how come i don't see any purple primer on those joints? do some states allow pvc cement without it?

DannyT

did someone drill a hole in the side of the 3 inch line from the toilet that's being siphoned and stick a 3/4 pvc line in the side of it? that's definitely not legal. if the stack was blocked it wouldn't be venting the other toilet either. technically the toilet on the left doesn't have a vent. where does the 3 inch horizontal line go that is between the joists? there should have been a wye in the line going to the toilet to pick up the drain from the lav and vent the toilet.

joecaption

Where's the clean out Wye?

TheEplumber

I'm with DannyT. The left wc is not vented. In fact, that whole stack would fail inspection if using UPC guidelines.
I would use a 4x3 fixture cross- then both wc's would be at the same inlet level. That would eliminate the 45.
Or as DannyT said- vent the left toilet to the lav
Probably at the base of the stack where it belongs.

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ben's plumbing

yep agree with eplumber amd danny t

Pirulo

Yep, left toilet is not being vented, I agree. And anyway, about that 3/4 pvc pipe glued on the side of the 3" one, kind of that p-trap they did tried to do should be called ****-trap, for the place is placed down the left toilet.

antinusk

Yes they did - they just screwed it right into the 3". It's for the water softener drain line. Originally, the hose was just laying in that "stack tube" and when the softener cycled, it would spew water out the top. So i put that fitting on the end to make a seal. I guess I'll eliminate it when I do the other work.
The 3" horizontal goes about 7' back to an elbow- presumably directly vertical as the stack. No cleanout on that elbow.

antinusk

There's a cleanout wye down below at just above floor level- the pipe that exits the house. Is that OK?

antinusk

Yep- I wondered about that, but it seemed to work since I sealed the end.

antinusk

So a 4x3 fixture cross- I'm guessing it looks like one of the wye fittings, but with an inlet from both sides? I like the sounds of it. Would that pass inspection then?
In order to get them at the same level, it looks like a total re-do from the flanges down to the stack pipe, right?
If there's a simpler way to install it, I'm entertaining ideas.