Blowing up two bottom drains (main drains?)

[PatPool]

Hi,
Our 20x40 in ground pool seems to have 2 main drains. One is in the shallow end (4ft) and one on the deep end (10ft). I am not sure if both of them are called "main drain". While blowing the lines during closing (in NJ) we saw bubbles/water moving on top where the drain is in shallow end but we never saw any water moving on top of the drain in the deep end. We used air compressor and waited 15 minutes, nothing.
Should we be worried? We didn't use any antifreeze, should we?
Thank you.

 

[mas985]

Are the two drains tied together? If so, the air will rise first in the shallow end because it requires less pressure to lift the water. Unless you can isolate the lines, it is unlikely that you would see any air in the lower drain. As long as you drain the pool below the frost line, you should be ok. Anti-freeze, is only necessary in lines that maintain some water and are above the frost line (i.e are at risk of freezing).

 

[RJPassan]

Are you sure they are both drains? We have a main drain (actually 2 side by side) in the deep end. In our shallow part we have 3 floor "returns"... not drains, in a line. The main drain and the skimmers are on one Jandy Valve (both take water in). The floor returns and wall returns are on another Jandy Valve (both put water back into the pool). I disconnect my equipment with unions and take my pump and filter inside for the winter. I then blow out my lines with a Cyclone Liner Vac (lots of air volume but low pressure). I only get air out of the first floor return in the line of 3 ...all the air comes out there, but they're all on the pool floor so it's fine.