Everything You Need to Know About Your Pool's Main Drain

If you stand at the edge of the deep end of your pool and look down, you should see beautiful, clear waters—that is, if your maintenance routine is on the mark. Below those waters, you should also be able to locate a drain at the bottom of your pool. It might seem like a simple device and easy to overlook, but that feature actually contributes to a vital part of your pool’s overall health—and you’re about to learn all about it.

I’ll explain what exactly your pool’s main drain is, how it connects to your circulation system, how it works, and how to assess whether or not yours is safe for swimmers. We’ll also go over how to fix a clogged main drain and how to plug it up for the winter. Get ready to know the answer to all your main drain problems. We’re going in.

What is Your Pool’s Main Drain?

The main drain is that vent-like square or circle located at the bottom of your pool, though ideally yours has more than just one—more on that later. Basically, it sucks in water, similar to the skimmer on the side of your pool. In fact, the skimmer and your pool’s main drain work together to keep your pool water circulating, healthy, and clean.

Your pool’s skimmer gets a lot of air time, but the main drain is the primary way that water is drawn from your pool into the pump and filter.

How Does Your Main Drain Connect to Your Pool’s Circulation?

In order to understand how your main drain connects to your pool’s circulation system, let’s debrief on how water moves through your plumbing and equipment. Spoiler alert: the main drain is the first step to circulation (though circulation by definition is ongoing!).

First, your pump sucks in water from the pool through the main drain (!) and the skimmer. Next, water passes through the pump’s strainer basket, which catches large debris like leaves. It also passes into the filter, which cleans the water of microscopic debris and contaminants. Finally, the water passes out of the filter and back into the pool through the pool jets.

It might be hard to see, but your pump is moving an intense amount of water through your system—especially if you have the right-sized pump for you. Ideally, your pump’s turnover rate is about eight hours, which means that all of the water in your pool goes through the above steps in that time. Now consider the fact that most pools contain around 30,000 gallons of water—that’s a lot of movement!

Without the help of a main drain, your pool wouldn’t be as efficient. Your pump needs to be able to suck in a lot of water to keep its turnover rate on the mark. Thankfully, your pool’s main drain makes it happen.

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How Does Your Pool’s Main Drain Work?

Again, your pool’s skimmer comes in handy when describing how a main drain works. Much like a skimmer, your pool’s main drain is an outlet that houses a pipe which runs to the pump and connects to the larger system. But how it actually works—just like every other part of your circulation system—is entirely reliant on the pump. When the pump isn’t on, water isn’t actively being sucked from the main drain. Instead, it’s more or less stagnant on the drain, though without plugging the main drain entirely, some water will lazily work its way into the pipes. That’s why it’s important to plug your drain before the winter—and I’ll explain how to do that later.

How to Tell If Your Main Drain is Working

If you’re not sure that your main drain is working, well, make sure the pump is on first! Again, it’s the pump that powers the drain. And if you’re still not sure whether or not your main drain is pulling in water, all you need is a leaf to be sure.

The test is as simple as this: put a leaf on your main drain. If it floats around a bit, your main drain isn’t working, which usually means that it’s clogged up with debris. If the leaf sticks, your main drain is in working order. Booyah.

Do You Have a Safe Main Drain?

Here’s the immensely unfortunate thing about main drains: they have actually been the culprit for a fair amount of tragedies, specifically the drownings of humans and animals.

In order to understand why this seemingly harmless feature has caused these tragedies, consider how a main drain works. When the pump is on, it’s sucking a large amount of water—again, more than the skimmer—through your system. That means that it provides a high amount of suction. If swimmers or animals are on the other side of that suction—especially those who are smaller in size—they could and have gotten trapped against the drain.

That being said, this devastating outcome is happening a lot less often. That’s because newer pools are being designed with this hazard in mind, and usually have at least two main drains as a result, which cuts the suction power in half and significantly reduces risk. It’s also recommended that your main drain have an approved cover—otherwise, they look like big holes and are too powerful for swimmer safety.

In order to assess the safety of your main drain, first make sure that you have at least two. If you only have one, it’s important to take extra precautions. Any swimmers with long hair should tie theirs up into a ponytail or bathing cap, and all jewelry should be removed prior to entering the pool. It’s also essential that no swimmers play with or sit on either the main drain or your pool’s wall vacuum fittings.

And if your main drain cover is missing or broken, don’t allow anyone to enter the pool. No exceptions—it’s just not worth the risk.

Keep your pool as clean as possible—and prevent main drain clogs—by switching to a powerful automatic cleaner that works on its own. Look no further than the Blue Torrent MyBot Inground Robotic Cleaner, which works powerfully to keep your walls and floor sparkling clean. As customer David Lain says, “Very pleased. My wife loves it.” Check out this user review to find out more.

Can You Use a Main Drain to Drain Your Pool?

It’s a bit confusing, I know, since “main drain” is its name, but main drains aren’t actually used to drain pools. The word “drain” actually refers to water moving to your pump. Main drains only direct through your circulation system—not away from it. You’ll have to use a submersible pump for that job.

How to Fix a Clogged Main Drain

That leaf trick I showed you earlier indicating that your main drain is blocked? Debris is probably the culprit. Here’s how to unclog a main drain:

  1. Power off your pump and disconnect it from its power source. This is absolutely non-negotiable—and the only way to unclog your main drain safely!
  2. Time for some deep-end diving. Remove your main drain cover. This will take a few tries. Don’t try to stay underwater more than your lungs allow. I even recommend having a buddy watch over this process, just in case.
  3. Once your main drain cover is off, place a pool plunger over the drain. Push down on the plunger, then lift up. Repeat this motion several times to force the clog up and out of the drain.
  4. Next, place the drain cover back on the drain, and use an automatic cleaner to vacuum all the junk that you’re now swimming with (sorry about that!).
  5. If clogged after this process, it’s time to drain your pool and pour down a safe-for-pools drain cleaner into your main drain. This will help break down extra debris that your plunger didn’t pull up. Then, go ahead and refill your pool.

How to Plug a Main Drain

If you live in a place with freezing temperatures, it’s recommended that you plug your main drain before closing down your pool for the winter. That’s because the main drain could leak water into your system, even if your pump isn’t on. If that water the freezes, it expands, and could potentially crack your plumbing. Since your pool’s circulation operates using a significant amount of suction, any crack in your plumbing is going to present some major problems, including a total burst.

To plug a main drain during the pool winterizing process, first make sure that your pump is off and disconnected from power. Next, use a screwdriver to unscrew the lip of the main drain lid and take the lid off. Locate the small hole at the bottom of the main drain, and plug it with an expandable rubber plug or, if the hole is threaded, a plastic threaded plug. If you can, replace the main drain lid again. That’s it!

If you do need to drain your pool, the main drain won’t help you. Instead, you want a powerful, reliable, and heavy-duty cover pump like the BLACK+DECKER 1500 GPH Automatic Submersible Pump. Check out this user review to find out more.

Wasn’t Too Draining, Was It?

There you go: everything you could ever want to know about your pool’s main drain. Since this piece is essential to your pool’s circulation system, you know that much more about the overall needs and operations of your pool, too. And most importantly: you can swim even more safely. That’s what it’s all about. Enjoy.