New toilet is siphoning my sink

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dgmorr

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Hey guys,

I just installed a Toto Drake in my guest bathroom. Long story short, I plunged it and used a half gallon of dish soap after noticing it didn't flush as well as my powder room Drake, after this it works as I expected. This bathroom doesn't get used very often so I never noticed it was slow with the 30 yr old toilet (I only bought this house a year ago).

So with the thunderous flushing power of the Drake, I just noticed that my sink trap in the same room is being siphoned. I took an inspection camera down and it is being sucked enough to lose the air lock. Is there anything I can do to prevent this? The vent goes up the wall behind the sink and takes a long horizontal path through the attic and eventually through the roof. Can I add a junction in the piping in the roof just before it goes horizontal to add another vent through the roof to let more air in?

Not sure if this toilet is too powerful for the vent design, no clue on this? It's a 2" ABS vent.

The bathtub takes a more direct path to a different 3" stack, not sure why, but it uses the same vent line. The tub is not being siphoned. I'm assuming that the sink is the path of least resistance.

Thanks
 

Terry

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The quick fix would be to add an AAV after the lav p-trap. Sometimes in Canada they do an S trap, illegal in the US because they can siphon.
 
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dgmorr

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This just came to mind. While testing the tub after I installed it, I filled it up to the overflow then let it drain. The sound it made was similar to someone chugging a large drink. Sudden rush of water, then a slow down as if it had to let more air in, then another sudden rush. It would do this until a small whirlpool formed in the drain when the water was about 4" high.

Perhaps the vent for this bathroom is plugged up. I've never filled that bathtub before, and only used the old slow toilet a handful of times.

I'll sever the vent pipe in the attic and see if it speeds up at all before renting a long auger.

I don't have any room to add an AAV after the traps, I am using two pedestals. Would adding a Tee in the vertical portion of the vent allow the vent to work better(whether or not the single vent is blocked)? Basically have 2 x 2" vents up on the roof feeding the same single vent line inside.

Sorry for the use of technical terms ;)
 

dgmorr

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You sound very certain that it's not undersized vents, can you elaborate as to why? Does the length of the vent dictate the diameter of the vent?

It's basically been this way since 1985, presumably with no issues. Any clue why this would happen after changing the toilet? Coincidental with falling leaves clogging up the vent? Not sure how common that would be, 2" is a pretty small target. I have yet to sever the pipe in the attic for testing though.
 

Terry

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The Drake flushes much quicker than the old units with the standard 2" flush valve. They show up plumbing that may be suspect.
Are you sure that the lav has a vent?
 

dgmorr

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I know the sink and tub have a vent as I had the wall open while replacing the tub. I am not certain if the toilet has a dedicated vent.

The sinks drain into a vertical ABS pipe which runs into the wall then in the floor. I believe the toilet uses the sink drain line as the vent. As long as the sink is not draining, the toilet should have a clear vent line. Does This make sense? I haven't had the floor open so I can't see how it connects to the toilet waste line, but based on how I can hear the water, it would be something similar to this. Aside from opening up the walls again is the only way to correct this to put an AAV on each sink leg? (assuming the vent is not plugged) Upon further reading, I believe this is called a wet vent.

toiletsinktubwetvent.png


The tub takes a different path to another stack in my case, but shares the same vent as the sink.
 
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dgmorr

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I went up in the attic and found that the vent line had a low spot that filled up with water. It turned out to be just a combination of a new place, never using the bathroom, a new toilet and improper slope on the vent. Not sure how water got in there as that line meets the vertical stack out the roof at a 90* tee - condensation? Either way, I can sleep now with no more siphoning.

Thanks
 
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