Plumbing roof vents, modern vs. old style

[Hassin Bin Sober]

7. How's the toilet flushing?

A lot of times gurgling is a sign of backed up main drain line. The lower fixtures usually show signs first.

If it was a main vent problem you might notice it upstairs too. My buddy’s condo had a clogged roof vent and his downstairs neighbor flushing her toilet caused his shower trap to gurgle - even to the point it sucked his trap try.


Or it could be as you suspect. It could be a local obstruction in the vent that joins the main stack above and behind your sink. If one exists. But that seems less likely.


The sink may not be vented at all - just relying on the diameter of the pipe to allow free flow. If the pipe is partially obstructed this could cause a gurgle.

You could try an under sink air admittance valve vent that come attached to the trap. About $20-30 bucks on Amazon. Though they don’t meet code in many jurisdictions, they can be a solution for unvented fixtures (in islands or basements etc.).

My bet is main line obstruction. Are you on a basement or a slab?