The clearest signs are gurgling from drains or toilets, slow drains across several fixtures at once, and sewer smells inside the house. They happen because a blocked vent starves the drains of air. A clogged main line causes the same symptoms, so the first job is ruling that out.
Draining water needs air behind it to flow smoothly. With the vent open, that air enters from the roof. With the vent blocked, moving water pulls air from wherever it can, usually through the water in nearby traps. That produces the gurgle, and it can pull a trap dry, which lets sewer gas into the room.
Other clues include a toilet that bubbles when a nearby sink or tub drains, a bowl water level that drops on its own, and a smell that gets worse on still, humid days. In DFW, fall leaves and spring bird nests are common causes at the roof opening.
None of these signs prove a vent clog on their own. A partial clog in the main sewer line causes the same gurgling and slow drains, and it is worth ruling out first because it can end in a backup. If a drain cleaning clears the symptoms, the vent was fine. If the gurgling returns with a clear line, the vent is the next place to look.
Nuflow DFW is a licensed trenchless sewer contractor serving 25 Dallas-Fort Worth cities, RMP# 46694. Our drain cleaning rules out the main line first, and a camera inspection confirms what is left. You keep the footage. Call (469) 701-0597.