Main Drain - How can blowing it out leave it water-free?

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,063
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
This is exactly what my Dad always said when he was still here and helped me winterize the pool. I'd personally never take a chance on it cause we're not talking about just the drain area but the much smaller pipe that goes up to the skimmer.

Glad me and your Dad agree.

That's why you need to winterize the pipe that connects to the skimmer by stuffing foam rope down it until you are below your frost line.


Frost_Line_Map.jpg
 
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Catanzaro

Platinum Supporter
TFP Guide
Jul 30, 2014
3,495
Monmouth County, New Jersey
The main drain is the least important of all. Think about it, water expands when it freezes at 9%, so and you are literally 8' down in the ground, where the ice can expand through the drains at the bottom. How many times have you seen water freeze 8' down or even 4' to 6' down? As long as you remove most of the water, the lines will be fine. You can even place a winter plug in the pump basket housing to create a further seal, but sometimes the valves leak. With the Cyclone, a modified cover, or some adapter, 30 seconds of air bubbling from the drains, and creating the air lock is all you need. No sense in paying someone to clear the drain. I think the first year, I clear the drain 3X for a total of 3 minutes, just to make sure. Now, 30-45 seconds, lock and call it a day.
 
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Catanzaro

Platinum Supporter
TFP Guide
Jul 30, 2014
3,495
Monmouth County, New Jersey
?? Not sure what you're referring to...if I were to stuff something down in there I wouldn't be able to use my double plug.
Some pool owners use foam rope to compensate for expansion. The "air lock" is designed to keep water out of the lines. Often times the valves leak, causing water to come back in, but again, this is the least important unless water freezes deep 6'. And there is always room for expansion on the bottom of the pool floor. If water were to freeze, it would start from the highest point and work its way down. This would force ice to push water out from the bottom. I would not place too much emphasis on the MD. The skimmers are the most important, with the returns next.
 

anthonypool89

Gold Supporter
Aug 26, 2016
957
Berks County, PA
The skimmers are the most important, with the returns next.
Agree completely. I've never seen the ice on the pool more than a few inches thick. I always keep an empty gallon container in the skimmer pot as expansion material - and that will at times get completely caked in with ice around it. As to the return lines - except for the fact that without plugging them water would fill those lines up to surface level and beyond (and so they DO need to be winterized), otherwise where the return lines enter the pool, I'm betting (at least in my area) the water would never freeze down that far.