Sometimes it’s not that water can’t get out, but that air can’t get in. Imagine turning a full bottle upside down to empty it—the liquid “glugs” out in fits and starts for just the same reason. Tilt the bottle over slowly to let air in and the liquid exits smoothly.
Properly vented plumbing lets air into the drains so that fluids flow well and traps aren’t sucked dry by the vacuum action of rushing wastewater. Vent pipes also let fetid, dangerous sewer gases out. The pipes link the drainage system to the stubby little pipe—part of the waste stack— that sticks up through your roof. An obstructed vent is not overly common, but cottage vent pipes can be clogged by snow or vegetation, as well as animals and their nests or food caches.
The gurgle test
It can be tricky to diagnose a blocked vent. A drain that’s sluggish even after you’ve snaked it, or one that gurgles when you pull the plug, hints at vent problems: The system is struggling to admit air via the fixture rather than the vent. Another sign is smelly sewer gas escaping the drain—without a working vent, water running down the pipes can siphon the trap dry. Sometimes you can spot a blockage by peering down the pipe from the roof (bring a flashlight).
You can snake the vent from above with a manual or drill-powered snake. Pros may use an electric snake, but I don’t recommend lugging a heavy and awkward power unit to your roof. If you don’t have a plumbing snake that’s long enough, you can try feeding in a cold, stiff garden hose to flush or push the blockage down. Before you turn on the hose, station a helper inside, ready to yell if water starts backing up out of a fixture. Rigging a narrow extension onto a shop vac hose may let you suck out the problem, bit by bit. In any case, pushing a blockage down into your drains is not nearly as desirable as pulling one up and out.
Tip: To keep a food cache or leaves out of the vent, you can cap it with a cylinder of chicken wire. But if snow then gathers on the cap and affects air circulation, condensation can freeze in the pipe and block it. In that case, remove the cap as part of your closing-up chores.