I have an ancient craftsman 4 horse  compressor.  It won't die. I want to replace it, but it won't die.  I put it in a rather inaccessible location and ran hoses and a remote switch. Draining it was a PITA till I figured out that there's no harm in a little leaking air from the drain plug so I just leave it cracked a scosh. So I don't  drain it.   

I always forget to drain mine. Thanks for the reminder!

 LIving where the humidity is low has its advantages and I don't get much moisture in my tank.

However, it don't take a lot to get in your lower lines and piping. There it can freeze and burst tubes and valves.  I know, I forgot and it did. I insulated my garage and now it no longer freezes, provided some idiot like me don't leave the door open

If you think about it, when the compressor runs on certain days, more moisture is formed than other days. It forms on all the areas inside the tank. If the walls get to much moisture it drains down hill the the outlet. You turn the knob and drain whats right there leaving moisture still on all areas inside the tank.

Very expensive tanks might be coated inside after the welding was completed but not all were done that way. Thicker walled tanks will last a long time before they start leaking I have use an 80 gallon with a plate welded on it saying it was made in 1957 with ASME specks. It still runs great. I got it used in about 1977, give or take a year or two one way or the other. It had been on the back of a tire service truck then had been in a wreck and turned over throwing the compressor out on the highway. When I got it it needed the copper pipe going from the pump to the tank and a few other things were ruined. I have it sitting outside under a tin cover against my shop. It gets drained maybe two times a year and still has never rusted a hole it the tank ...   My feeling, no matter how many times you drain a tank each day, moisture will still be on the walls even though you do get water maybe every time you turn the valve.

   I have a 120 gallon monster compressor sitting in reserve that was built in 1954. It hasn't been run for about 8 years but didn't leak the last time I hooked it up to electricity...

   We use to stock an automatic drain for compressors . It was made by Sioux.  Some of the finest impact wrenches, grinders and other air operated equipment. This was in the sixties and seventies and don't even know if they still exist.. but really what you are doing is okay as long as hardly any air is leaking and don't bug you with the sound.

Mines in the shop. A 7 hp, 80 gallon two, stage. It has a drain at the hose connection just after the regulator and another at the bottom of the tank. I open both after every day's use and leave the pet cocks open. Humidity is low here in AZ but, there is always moisture draining out after a day's use.

It isn't used every day. If it weren't so blasted loud, I'd sure like to use it for sanding and grinding chores. And Patch, Sioux is still in business. My son buys their tools from the Snap on truck. 

 

12 hours ago, Cliff said:

Draining it was a PITA

 

replumb the drain for easy access...

Watch so that slowly leaking drain doesn't plug up...