Looking for a new lavatory sink? You may have noticed that many sinks have an overflow drain, but not all do.

So do you need a sink with an overflow drain or not?

Well, in short, overflow drains aren’t necessarily essential, but they do serve a couple of useful purposes, so it’s still usually a good idea to have one. 

Let’s talk some more about bathroom sink overflow drains to help you decide if you want one or not.

What Is A Bathroom Sink Overflow Drain & How Does It Work?

Let’s start by talking about what exactly a bathroom sink overflow drain is anyway. 

An overflow drain is a small hole in the basin of the sink, generally found high up on the inside of the front wall or rear wall. The vast majority of undermount and top mount bathroom sinks will have an overflow drain, but not all of them. 

Bathroom sink overflow drains perform two important functions:

Overflow Prevention

Overflow Prevention

First, if you leave water running from your bathroom faucet and it fills up the sink, the overflow drain will divert some of the water out of the sink and down the drain to help prevent the sink from overflowing. 

This is especially important if your pop-up drain cover is closed or if you’re using another type of drain stopper. It won’t usually help if your drain has a clog, though, since the outlet into the main drain pipe is typically right below the main drain hole.

There’s little chance of a clog forming in the small space between the overflow drain outlet and the main sink drain.

In addition, an overflow drain usually diverts less water than faucet puts out at full volume, so it only slows overflow, it doesn’t stop it entirely if the faucet continues to flow unsupervised. 

If you leave a faucet running, you still risk having water run out over the countertops of the bathroom vanity and onto the floor — definitely not the reason you want to have to do a bathroom remodel.

Draining Speed

Draining Speed

Second, an overflow drain helps draining speed by allowing air in the drain pipe to escape the drain pipe through the overflow opening while the drain opening takes in more water. 

If the sink is full enough to cover the main drain, the sink can’t take water in because it’s already full of air and water. The air that’s already in the drain needs a way to escape.

The water over the drain makes this harder because it blocks the air’s path, so the air has to slowly bubble through it, slowing the rate that water can drain.

If there’s an overflow drain, the air can exit the drain pipe through the overflow drain. The overflow drain shouldn’t have water blocking the air’s flow, which makes it much faster and easier for the air to escape. 

That way the water can flow through the main drain, while the displaced air can escape through the overflow drain.

Sinks With No Overflow Drain

Sinks With No Overflow Drain

As we’ve already said, most undermount and top mount sinks will have an overflow drain. Vessel sinks are the most common type of sink to not feature an overflow drain, though some do still have overflow drains. 

The main advantage is simply the style, if you happen to prefer the vessel style sinks. It’s also slightly easier to install from a plumbing perspective, but installing the actual basin of a vessel sink can be tricky.

For most of us, it’s not a DIY job and you’ll want to call a plumber to take care of it anyway.

On the other hand, you get less overflow prevention and the sink will drain slower. 

With that said, you should never leave a sink running unsupervised anyway since an overflow drain is not a foolproof way to prevent the sink from overflowing. That way you can just turn the faucet off if overflow is a risk.

The slower drainage should be the more frequently encountered problem, but it will typically be a minor inconvenience at most.

All of this is to say that no, you don’t need an overflow drain in your bathroom sink. An overflow drain can be nice to have, but it’s by no means essential.

How To Clean A Bathroom Sink Drain Overflow Hole

How To Clean A Bathroom Sink Drain Overflow Hole

If you do get a sink with an overflow drain, it’s important to know how to clean it to keep the overflow drain functioning at its best.

Overflow drains are typically low maintenance, but they can occasionally experience blockages. This is because it doesn’t get the regular flushing that the main sink drain gets and it’s especially likely if your sink is frequently filled with more than just clean water. 

The angle of the overflow drain hole can make it a little tricky to clean the overflow drain, but if you can overcome that, it’s a pretty straightforward process. 

Pipe cleaning brushes with flexible stems can help you scrub the inside of the drain, while a flexible hose attached to a funnel is useful for flushing the drain with water or other liquids.

The easiest way to clean your overflow drain is also the safest for your pipes. Pour one part baking soda down the drain, followed by an equal part white vinegar.

The fizzing action can help remove gunk build-up in the drain. 

Let the vinegar and baking soda do its thing for about ten to fifteen minutes. Then flush the drain with hot water to remove anything that the mixture has loosened up.

If that doesn’t do the trick, you can also try mixing one part chlorine bleach and one part cold water (hot water makes bleach ineffective) and pouring it down the overflow drain. Let it sit for ten minutes, then flush the drain with hot water. 

However, you should never use bleach if your home has a septic tank. Use a septic-safe enzyme drain cleaner instead. 

Final Thoughts On Overflow Drains

That’s about all there is to say on overflow drains. 

While they can certainly add convenience, they’re by no means essential for your bathroom. If you’ve fallen in love with a bathroom sink and the only thing holding you back is the lack of an overflow drain, don’t let it stop you.