How To Clean Out Plumbing Vent [upd] -

If you can't get on the roof, you can try these indoor methods, though they are less effective:

Plumbing Vent Pipes: Importance & Issues | AHS - American Home Shield how to clean out plumbing vent

If the water backs up out of the vent, you have a stubborn clog. Use a plumber's snake to break up the debris. Feed it down the pipe until you feel resistance, then crank and push to clear the way. If you can't get on the roof, you