Winterizing, how do you protect the main center pool drain?


Jul 24, 2007
The skimmers and jets can be cleared and capped with the water level below the jets. How do you clear the main pool drain? Do you need to fill it with antifreeze and how do you do this?
I have a powered pool cover and must fill the pool back up with water in order to support the cover.
Thanks for you help.


TFP Expert
LifeTime Supporter
Mar 29, 2007
Coastalish 'down easter'
Mfee, welcome to TFP!! :cheers:

MDs are somewhat troublesome to winterize. The best way would be to don SCUBA gear and plug the line while air was blowing through it. Unfortunately, that is rarely practical :( What I do, and every company I've worked for, is to blow air into the line from the filter pad until the MD bubbles for ~ 30 seconds and 'slam' the valve shut, with the air still on. This keeps the water that re-enters the line below the freeze line of the ground, hopefully protecting the pipe. No way to get antifreeze into the line, and it wouldn't matter - the antifreeze would mix with the pool water and be useless!


TFP Guide
In The Industry
May 14, 2007
New Brunswick Canada
Same here in the East of will normally only go down about 4 feet from surface...and as long as there is free area on either side of this ice, there will not be a break..the ice can move up the line towards the surface without restriction..and the same goes for down towards the drain....its when ice has to where to go, then its expansion will cause a break.

Its weird...our new pool...was totally plumbed with Spa Flex Hose, ice wont break it, but our neighbor was plumbed with solid pvc....which will break. Stupid thing is, its about the same price, so why PB's wont use this is beyond my comprehension.


Active member
Apr 25, 2007
I live in Iowa and for the past 15 years I have pumped about 5 gallons of antifreeze into the main drain line and just closed the valve. Antifreeze is heavier than water so it will sit towards the bottom of the drain. Freeze line here is 3.5 ft. and the main drain is about 9 ft. down. Maybe the antifreeze in the main drain line doesn't really protect it all that much but lets me sleep better at night knowng there is some protection.


Well-known member
May 14, 2007
Anyone ever try blowing out the main drain and shutting that valve. Then take a bag of sand and place this over the main drain. Then open the main drain valve and pour some antifreeze down the pipe and reclose. I don't know if it would make a diference but it may help keep the antifreeze from mixing back into the pool water.