PSC Ep. 92: How do I winterize my main drain line?

PSC Ep. 92: How do I winterize my main drain line?

In today’s episode of Poolside Chat, Rob and Matt tackle another common swimming pool question: 
I’m in the process of closing my pool. How do I winterize my main drain line?

Since closing the main drain isn’t the first step in the winterizing process, we’ll assume that the water has been drained below the skimmer and return jets. And that those lines have already been winterized.

There are a couple of different ways to winterize the main drain line and it depends on how the main drain is plumbed. We’ll start with the most common.

The majority of main drains have a line that runs from the drain back to the equipment. If you have this style, you’ll need a blower. The first step will be isolating the line that runs from the pump back to the main drain. This will require that the valve for the main drain is open and the skimmer line is closed.

With the pump lid removed you can insert the blower hose in the strainer housing and into the suction port. Turn the blower on and wait for the bubbles to emerge from the main drain. Let that continue for 30 seconds or so and with the blower is still running, close the valve. This will create an air pocket and the main drain will remain free of water.

So that covers the most common type of main drain line. But we’ve recently had some questions about another configuration.


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The other type of main drain line connects directly to a skimmer. Some skimmers have two holes in the bottom. The hole furthest away from the pool is the line that goes back to the pump. The hole closest to the pool would be the one that connects to the main drain. This is called an equalizer line. 

Since you drained the pool below the skimmer, the water level in the main drain pipe should be lower as well. If the water in the pipe freezes, it will expand up the partially empty line and not out. To close off the line, you can thread in a gizmo or use a plug. 

For some insurance, you can get some foam rope, also called foam backer rod, and feed that into the line before it’s capped. The closed-cell foam will compress and absorb the ice expansion and help prevent the ice from expanding outward.

If you have any comments or methods for winterizing a main drain line, please leave a comment down below. Please remember to like and subscribe and for all your pool needs, visit us over at

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