For the time being I have done what both of you are suggesting.  I made up an 18" long, 3/8" drain hose.  It has an elbow on the tank end and a ball valve on the other.  I'll use that until I decide to make or buy an auto drain. 

Telling myself to drain the tank is easier than actually remembering to drain the tank.

I bought a Husky drain extension. About $25 on Ebay. It's a 12" extension and has a quarter turn shut off valve on it. Works great. It's flexible so you can route it out where it's handy. So easy to shut the compressor down, open the valve, go in the house and drink a beer.

Auto is a fine way to go. But why not a simple self Ball Valve =  on a lever. Still Manual.

I don't compress ALOT but have a 40 Gallon that stays charged.  Sand blaster + air TOols.   YEs it makes moisture.  Once a week - to once a month =  Crack the floor ball valve quickly and it lets it out. 

I simply removed the Horrible stock 'wing' / screw  drain.. screwed in a 90 degree with a 4-5 inch pipe extension and ball  Lever valve on the end.  Worked for my setup and is a easy self drain.  

Just a thought.

I recently purchased a replacement air compressor since the tank in my old one rusted out.  I want to install an auto drain on this compressor to minimize rust damage.

I have used the Harbor Freight auto drain and it is OK until it plugs.  There are electric, timer based auto drains available but their timing doesn't seem right for a home shop.  Those timer based models also have a lot of complaints concerning stuck or plugged solenoid valves.

Do any of you use auto drains on your air compressors?  If so, are you pleased with them and what model would you recommend?

Thanks.