Q: I recently replaced the wax ring under the toilet. Now when I take a shower, the water level in the bowl drops and makes a loud glugging sound. (The shower drains just fine.) What could be causing this?

—Don Camp, Doraville, GA.

A: Richard Trethewey replies: When I hear "glugging sound" and "toilet" I think blocked vent. Water can't go down a drain ­unless there's a way to bring in air to replace it, so plumbing drains have vent pipes that go out the roof to draw in fresh air. If a vent is blocked or not connected properly, the vacuum caused by the draining will pull water out of sink traps instead—or the toilet, in your case.

I'm not sure why this is happening now and not before. It's likely not related to your repair, because it's hard to accidentally drop something in the vent from the toilet drain, where you were working. But vent problems can be a bear to diagnose; I'd have a plumber check the vent pipe. He or she might be able to snake it out from the roof. If that doesn't work, more invasive and expensive work might be needed to clear the clog.

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