Water level going down intoilet bowl

[CableGuy]

Hello,
I just bought a new home and have been having a toilet problem since I moved in. The problem is the water in the bowl will drain out by itself rather quickly. And sometimes soap bubbles will come up into the bowl I assume from the sink. The bowl will gurgle when the sink water is running.I'm on city sewer and have had 5 service calls by the plumbing company that did the work. Everytime they say it is something different. They have ran a sewer machine twice, replaced the toilet bowl, ran a camera from the clean out to the main, and snaked the vent pipe with no results. Now I'm being told the soap is the problem. This might explain bubbles in the toilet, but not the water being pulled from the bowl. I think the plumbers are grasping at straws at this point. The toilet, sink, tub, and shower are all connected to the same vent pipe. The other toilet in the house is working fine. I have had no backups anywhere, but I do get gurgling noises from from the toilet, shower and tub, depending on which one is being used (run the sink and the toilet gurgles). There is definitely a vacuum being created somewhere, if I take the caps off the cleanouts it will flush normally and the water will stay in the bowl. Anyone ever ran into this before???
Thank you in advance.

[Phelps]

You hit on it when you said it no longer does it when you take cleanout caps off.

The wind crossing the roof stack creates a venturi vacuum effect and wants to pull air up the stack like a chimney. On real windy days, you can sometimes see water slosh a little in the toilet bowl and lower some. This updraft causes it to pull the water right out of the trap in the toilet.

But you have a REAL problem. Apparently you have a blockage in the main line beyond the toilet.

Soap bubbles back at the toilet are due to an air lock in the sewer line (due to blockage) and it has a tendency to take a path of least resistance.

The reason the toilet flushes okay is that between flushes, the water in the sewer line slowly drains out. The obstruction could conceivably be all the way out by the road, where it dumps into the city sewer main. The plumbers maybe did not roto-rooter out far enough.

Test the theory by flushing the toilet repeatedly, back to back to back to back to back to back, etc.. I bet you wil find the water back up. Don't do this too many times without checking basement floor drains and laundry tubs that could start filing up with water.

[LazyPup]

The post states that the water in the traps is gurgling and the water level in the water closet is dropping below normal level. Both of those conditions indicate a negative vent air pressure in the horizontal branch line.

We can rule out an obstruction in the lines in two ways.

1. An obstruction would cause the drains to be sluggish and the water closet bowl to overfill and have an incomplete flush, but such is not the case.

2.All the lines have been snaked repeatedly and inspected with a camera, yet no sign of an obstruction was noted.

I suspect the problem is inadequate venting which would result in the negative pressure as noted.

In a typical layout they run a 3" horizontal line from the water closet to the stack or main drain. Off that 3" they run the horizontal waste arms to the tub and shower and those waste arms vent from the 3" branch line.

Normally we would then run a horizontal branch from the 3" to a riser running up behind the lavatory.

When it is necessary to create an auxillary vent to common practice is to extend the auxillary vent vertically from the sanitary tee behind the lavatory up to the roof, however that is not always required. It depends upon the total developed length of the lavatory waste arm.

Under the Uniform Plumbing Code the total length of the 3" from the water closet to a vent may not exceed 8', however under the International Residential Code there is no length restriction.

I suspect that the tub, shower and lavatory are presently set up to vent off the 3" horizontal branch from the water closet. In turn, the length of that branch line from the water closet to the stack or house main drain exceeds the diameter divided by pitch. 3" divided by 1/4" (3/.25= 12') thus the horizontal branch from the water closet to the stack is not properly venting and in turn the waste arms from the tub and shower cannot properly vent either.

To test this theory, disconnect the trap under the lavatory and try flushing the water closet and draining the tub and shower. If the water closet, tub and shower function correctly with the lavatory trap disconnected this confirms the need of additional venting.

If this is true, the proper method would be to extend an auxillary vent upwards from the lavatory drain to the roof, however most people would be very reluctant to begin opening walls to add the vent line. An altenative would be to install an Air Inlet Valve (studor vent) on the waste arm between the lavatory trap and the riser in the wall.

[Phelps]

I reread the first post again. I still am not sure. As surely as the plumbers said the sewer line is clear, they also said the vent stack is clear. I was thinking two-fold problem: Cracked trap in toilet + soap bubbles...but he said they replaced the bowl. Hmmmmm.

Where is that second toilet? On the other end of the house? Or, above or below the first toilet? I am wondering if the same vent is shared or if there are two.