Reasonable to assume I've got a clogged vent? (Video)

[Didymus21]

This fun little annoyance started a few weeks back after working on some of my plumbing. I moved a toilet in an adjacent bathroom, to include rerouting some DWV piping. The two toilets share a vent stack. The water from the bowl is siphoning out. Not completely, but it is obvious that it recedes once the bowl finishes filling. The other apparent issue is that it's readily siphoning while filling the bowl.

I've included a youtube link of the problem. Does it seem likely this is a clogged vent line, or could there be another issue?

 

[Terry]

Is the refill from the fill valve pointed down the overflow tube?
This is what refills the bowl. That would be the black tube in this picture.

 

[Sponsor]

 

[Didymus21]

Yes, that does not appear to be an issue. It continues to siphon while the bowl is filling and for a short time after it finishes filling.

Is the refill from the fill valve pointed down the overflow tube?
This is what refills the bowl. That would be the black tube in this picture.

 

[hj]

It is definitely NOT a vent issue, in fact, it may not even be siphonage since all the water is not "sucked" out of the bowl. It could just be the bowl stabilizing at its "design water level".

 

[Terry]

It is definitely NOT a vent issue, in fact, it may not even be siphonage since all the water is not "sucked" out of the bowl. It could just be the bowl stabilizing at its "design water level".

I'm inclined to agree. The bowl level is determned by the top of the bend that leaves the bowl. The water won't stay any higher than that.

 

[Didymus21]

Hmm...I can't rule out the possibility it was always like that and I just didn't notice until I worked on the toilet..

 

[WJcandee]

Have you ever replaced the fill valve? It looks like the fill valve is overfilling the bowl a smidge. After which it settles to its design level (everything else just spills over the weir). Some fill valves refill at a different percentage than others, and some allow for refill percentage adjustment (like the Korky 528MP).

As the others have noted, all this is is the bowl settling to its design level. If the old installation tilted the bowl forward significantly, or the new one tilts the bowl back significantly, this can change the settle level because it changes the position of the weir of the toilet vis a vis the water spot. But only if it's a significant tilt.

Here's a cutaway that explains what is happening. If it overfills, it just spills over the weir and settles:

PS Blue food coloring would be more appealing next time. Ick.

 

[Didymus21]

PS Blue food coloring would be more appealing next time. Ick.

Hah...yeah I know. I only had coffee on hand. I'll adjust the fill valve a bit. Thanks.

 

[WJcandee]

If your fill valve doesn't let you adjust bowl refill independent of tank refill, I would just leave it alone, presuming that your tank fill is about 1/2" or a little less below the top of the overflow riser. If you can independently adjust refill, just back it off a smidge. Better for the next flush that you slightly-overfill than you underfill the bowl.

 

[hj]

IF it is what we think it is, there is no adjustment, other than to reduce the flow of the incoming water.