My first floor bathroom sink drains through vertically down and then through a sloping pipe and then into a septic system. The sink drains very slowly. The other sinks and two showers in the house are OK. I first thought the sink line was clogged, but I have opened and cleaned out the line and also, when I use a small sink-size plunger in this sink and get the water moving it then drains well. I can even add more water while the sink is draining and it still drains well. However, a while after the sink has drained, it is slow again. When the last of the water leaves the sink there is a gurgling sound from the trap at about 2 gigrles per second, and the rate slowly decreases until it stops.

It seems to me that the vent, which is perhaps 6 feet down the sloping pipe may be clogged and has created an air trap in front of the waste weater. That would explain why the water drains well after I have started it moving and also why the sink trap gurgles as the last of the water drains from the sloping pipe - it is pulling air through the trap.

Does this make sense? How do I get rid of the air trap?

Very good Robert, Go to the head of the class. You have analized your problem every bit as good as I could. You indeed have a clogged vent. The sound you hear is the trap venting. The answer, of course, is to snake out the vent. Don't forget to wash it down good or the clog might end up in the sinks drain line. Good luck, Tom

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Originally Posted by speedball1

Very good Robert, Go to the head of the class. You have analized your problem every bit as good as I could. You indeed have a clogged vent. The sound you hear is the trap venting. The answer, of course, is to snake out the vent. Don't forget to wash it down good or the clog might end up in the sinks drain line. good luck, Tom

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Thanks for the confirmation. Now I just have to figure out how to get up on the rooof so I can clean out the vent :)