Blowing out main drain


New member
Oct 27, 2010
Hi all,

When blowing out the main drain how do you know if an airlock has been achieved? I blow out the drain using a compressor, let it bubble for about 45 seconds, but after I close the valve I still get some bubbling here and there for a while. Is this normal or is the valve not closing properly perhaps? This is the first time I've closed the pool myself and I really don't want to screw it up



LifeTime Supporter
May 3, 2008
Montgomery County, PA
I think your OK. If you had a leaking value, you would be losing pressure and the weight of the water would force the air back into the pipes, instead of out of the drain.

I'm not an expert, so hopefully others will weigh in.


TFP Expert
May 20, 2007
South Central NJ
Most drain lines run horizontally before going up. This section usually refloods untill the rise in the line is above the drain. An air lock will prevent any further water from entering the rising pipe. That elevation is typically well below the frost line by several feet.