Vacuum in sewer plumbing?
Howdy All--
Whenever there's a serious storm with 40-50Mph wind velocities around my house, the standing water in one toilet bowl disappears.
Under ordinary conditions, all the drain fixtures function perfectly-- that is, the sinks drain in a flash. None of them gurgle or make unexpected noises. The toilets flush perfectly.
None of the traps are affected by flushing the toilets or draining the sinks.
But when gale force winds come in from certain directions one toilet bowl loses it's standing water. The water isn't blown out, it's sucked away as if a vacuum forms in the sewer line.
The toilet that empties is a "US goverment" toilet-- i.e. 1.6gal flush toilet, "low boy" type unit.
The other toilet in the house is non-goverment mandate flush. During these wind storm conditions it isn't affected although the standing water jumps around a little, but never clears.
There are two vent pipes that exit the two storey roof. Both pipes are 2" diameter below the roof, and exit as 3" pipes at the roof line. Vent pipes extend about 24" above the roof surface.
Main house DWV system is 4" PVC, with the "government toilet" on a 3" pipe branch that's about 6 feet long. This 3" pipe branch is vented by a 2" vent pipe that's 21 feet long straight up and exits at the roof.
My guess is that when the wind gusts hard enough across the vent pipe opening it causes a low pressure to build in the vent pipe. Column of air in vent pipe then acts as a piston that creates a short vacuum burst in the house drain system. Low flush government toilet has shallow trap that's finicky to slight pressure changes in DWV line. Negative pressure causes trap to drain.
Under "ordinary" condtions and wind velocities, no-effect on standing water in either toilet bowl.
Thoughts anyone? Fix for this?
THANK YOU for your attention!
