back siphoning and vents back to back

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steverw

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hi, I have put in two water-efficient toilets to our house because of the drought and water rationing, and noticed on both that after the filling is done, the bowl water level drops over about 30 sec by almost 1/2 inch, reducing the water surface area and depth by quite a bit, considering there isn't much there to begin with. As an experiment I opened the main house trap near where the house tree of pipes connect to city sewer (or is it called cleanout?), and the bowls don't drop level any more. So I think this means that the venting isn't working properly. I was going to go out on the roof and snake the 3-4 vent pipes up there, but decided to check in with this forum first in case snaking could hurt things more than help. This forum has been very helpful as I've shopped for toilets. Most of the posts about venting seem to be for new installs, any advice for diagnosing this kind of problem for one that's already done (house was built in1984)? note the old toilets were 3.5 gal, so the siphoning might have been there before and I just never noticed. also I suspect the two toilets are going into the same drain pipe line, since they sit just on the other side of a wall from each other. Possibly also two sinks, a bathtub and a showerstall tie in as well The pipes looked to be 3" at least when I had the toilets off. The vent pipes on the roof look a lot smaller.

so what do you think, OK to snake the vents from the roof with a $30 25' snake tool from Home Depot?
 

Terry

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back_to_back.jpg


With the new bowls and back to back installs, often its water being pushed out of the other bowl during a flush. Water skips across the double santee, pushing air with it. If you go into the other room, you will see the water leverl rise in the bowl.
When that happens, water drops over the high point of the trap and down the drain.
Watch the bowl, and have someone flush the toilet in the other room.
 

steverw

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back_to_back.jpg


With the new bowls and back to back installs, often its water being pushed out of the other bowl during a flush. Water skips across the double santee, pushing air with it. If you go into the other room, you will see the water leverl rise in the bowl.
When that happens, water drops over the high point of the trap and down the drain.
Watch the bowl, and have someone flush the toilet in the other room.

the toilets are not back to back, just near, maybe 4 ft. when the bowl was off, i stuck my arm down to clear out some sludge, the join with the main line was 1/2 arm length deep, didn't see/feel any other connection at the same place. In my case, the bowl level drops in the toilet that was just flushed, but only after the filling is stopped and the tank is quiet. On one bowl you can hear water dripping from under the bowl while the level is dropping. I did snake out the vent line, seems to have helped. We live at the top of a 700 ft hill, could that cause the city line to pull air continuously?
 

Reach4

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Interesting.

If you open that cleanout again or go up on the roof, it might be informative to put a smoking rope etc near the openings to see air flow. I don't know what knowing that would tell you.
 

hj

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I am not sure that I like the new format, and it appears many previous replies were deleted during the change over. If it were a vent problem it would only be a factor IF you were using water elsewhere in the house and creating a vacuum or siphon. From what you describe that is not happening.
 
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