Main Drain Winterization


In The Industry
Sep 19, 2019
Here in Ontario, pools are drained to just below the lowest jet and/or vac line (which is aprox 3'-0" down)

1. Pools which have a main drain connection to the skimmer:
-blowing out here is impossible as the water level will level itself out to the same level of the partially drained pool.
-I usually just add a good amount of foam rope and cape the line in the skimmer.
Is this sufficient to protect this line?

Pools which have a main drain line directly connected to the pump:
-I use 5HP shop vac blower to attempt to blow out the line, but not strong enough to push air bubbles out of the MD.
-my understanding here is that, the water in the line will level itself out to the same level of the partially drained pool, leaving air between that level and the pump.
-is this safe enough to protect the line from freezing?
-should I place foam rope down the line at the pump connection?
-I feel adding anti-free will just mix with the water in the line below and dilute itself rendering itself useless for freeze protection
-any tips here is welcomed.

3. Heater plugs - after blowing the heater out, is it best to leave the plug hole open, or place the plug back? (placing the plug back may give the interpretation to a client that the heater was not winterized proper, so I always leave them open, but I believe the owners manuals recommend closing back up. Any thoughts on this?


Silver Supporter
Jul 8, 2013
Columbus, Ohio
I use a Gizmo in the skimmer. It screws into the skimmer line. The top of the Gizmo has a opening with a plug. I pull the plug and vac/blow out the water in the skimmer end and the pump end of the line. I add anti-freeze and put the plug back into the Gizmo. I add anti-freeze to the pump end and plug it with a rubber plug. I open the main drain line at the pump end and blow the level down as much as possible. I add anti-freeze quickly before the water level can return. That way the end of the line is all anti-freeze for a considerable length. I plug that line with a rubber plug. I blow both return lines and cap them. They get anti-freeze added to both ends of the lines before they are capped. I don't drop my water level at all. That's worked for the last 20 years.

I don't have a heater so I can't help you there.


Platinum Supporter
TFP Guide
Jul 30, 2014
Monmouth County, New Jersey
If you clear the lines properly, then no need to remove plugs from the heater. If the shop vac does not have enough air volume, then you may be able to find a blow-thru plug to clear the main drain and push water below the frost line. Some people use rope, but I am a big believer of using trapped air for the main drain.

I would use antifreeze only in the return lines and the skimmer lines, not the main drain line.


Silver Supporter
Jul 8, 2013
Columbus, Ohio
I reread my comments. I put anti-freeze in the pump end of the main drain line and blow the water level down with a shop vac. Add a rubber plug before the water level can come back up. I'm relying on the anti-freeze and the trapped air. I also pour anti-freeze on top of the rubber plug to make sure the plug is air tight.


New member
Nov 3, 2019
Here is the hose set-up I used with the Cyclone blower for a Hayward pump. It is a 2 inch vacuum hose. The black rubber connector/reducer I got at Home Depot, comes with clamps. The 1.5 inch elbow is for the main drain inlet at the pump. I need to add a gasket for the elbow outlet, but this worked great.