No air bubbles come up out of the drain even though plenty of air pressure is being directed down into the line. I have the return lines plugged, and now am ready to blow out the skimmer and drain. The air directs down into the skimmer from the tank. (I use an air compressor attached to the top of the tank) so that I can blow through the whole system. When the air is directed down to the drain, NOTHING comes out - no air bubbles. I tried it over and over again. The line from the drain to skimmer can't be clogged cause I was running the pool from the drain once the water level got below the skimmer (I put a tennis ball in the skimmer against the pipe opening so it sucks only from the drain so as to get the water level a few inches below the skimmer). So nothing should be in the line. Just to make sure I got a tape measure and put it down through the pipe - it went in to around 13 feet - probably all the way down into the drain. So, what do I do now? I cannot for the life of me figure out where that air is going. If I pull the plug out part way from the skimmer, a huge amount of air comes back up. I can't go further until I blow out the drain. I've been doing this for 25 years and never had this problem. The plug I use in the skimmer is a double plug so you push it down part way so that the top plug plugs the skimmer, and then when the drain is blown, you push it down the rest of the way so both plugs are in place. I'm sure you're familiar with this system. I really don't know what to do. Hope someone can help.