How To Drain
       The Compressor Tank

You want to know why and how to drain the compressor tank?

Every time you use your air compressor, it is inhaling free air. That free air contains water vapor.

As the air pressure in the tank increases, the amount of air crammed into each cubic foot of space inside the tank increases too, and as a result water vapor in the air condenses into free water during the process.

Fill Your Tank

Run your compressor long enough without draining the tank and you will completely fill your air tank with water.

Here is more information on where the water comes from.

Drain Location

Every compressed air tank will have a drain valve, since every compressor tank will have to be drained regularly. The drain will be located in the lowest part of the tank when the compressor is sitting in its designed position.

That means that the compressor is oriented in the way it is supposed to be. You do not want to turn an air compressor on its side, anyway, though that is grist for another article.

Since gravity works, the water that condenses all over the wall inside your air tank will flow to the lowest spot in the tank, so that is where they put the drain, clever designers that they are.Drain Appearance What does the typical tank drain look like? All of the manual air tank drains that I have seen have a common appearance. You can see one in the photo below. compressor tank drain valve

I suppose your auto drain might look a little different from the one in the photo, but do not let that worry you. They all work in the same manner if they are a manual tank drain.

How Do They Work

You see the knurled ring at the bottom of the drain valve in the photo? That ring is knurled (has bumps on it) to provide a gripping surface for your fingers.

You turn that ring in a counter-clockwise direction (at least on mine, yours may turn the other way) to open the drain, and turn it the opposite way to close it.

All The Way, Please

When you drain your compressor tank, open your drain valve all the way.

If you just open the drain a little what I have had happen is that you will hear air escape, and then it might stop. You may think the tank is drained. What has really happened is that the water or debris in the bottom of the tank has blocked the drain. The tank is not empty of water at this point.

Open the tank drain all the way and be sure to void the entire tank of water.


Get ready for a surprise! The stuff that flows out of your tank will be water...yes, and it will also contain residue of compressor oil, perhaps a smidgen of tank rust, all spiced with whatever dust migrated into the tank through the intake filter. The water draining from your tank may be brownish in color.

So no, you do not want to drain the tank onto something you don't want stained, perhaps your garage floor?

I do drain my compressor tank on the floor of the garage. It is not a nice puddle, but the water evaporates and the rest of the gunk dries out on the floor and doesn't seep into the ground. It does, however, stain the floor.


I wear a pair of work gloves when I open the drain valve on my compressor tank.

I do not need or want that gunk all over my hand, which will happen if you do not wear a glove with the hand that is opening the tank drain.


As a general rule, drain the compressor tank after every use.

As soon as you compress air you have water in the tank. If you do not drain that water it starts rusting the tank from the inside, almost regardless of the coating that is applied to the interior of the tank at the factory.

These days the tank factory is in a different country, the metal might be recycled pop cans, and the quality of the coating inside a compressor that retails for $150 is pretty suspect I should think.

Drain your tank after every use. Slow down the eventual rust through that will happen with every low cost compressor air tank.

Open / Closed & Don't Forget

I generally leave my tank drain open until I go to use the air compressor again. Some folks do not.

It just seems logical to me to allow outside air access (yes, I know it's limited) to the tank to help dry it out.

But, do not forget to close the drain when you next go to use your compressor. These DIY type air compressors are very loud, and you may not hear the air you are compressing busily exiting the tank as it is being compressed, through the still-open tank drain.

If your compressor will not build air pressure, that is one of the first things to check.

Drain your tank!