How do i keep my New air compressor tank Dry?

drain it after every use ....................................

The zillions of cubic feet of air that the unit sucks in and compresses, contains humidity, which is water vapor, which condenses in the tank and the result is water. 

So drain it regularly.

My steel cook pot has water in it for months. Yeah I should wash the dishes...next time. Steel does not rust.   However your air tank is make of low quality steel so it rusts.

Now run away and go to a mirror and breathe on it, real close with a hot breath.   What happens is it gets foggy or steamy.  That is humidity in you.  There is humidity in the air you breathe so the compressor gets hot and out comes humid air.  Some guys run into a second tank FIRST to cool off the air and dry it out some and then it is piped into the first tank.  That air is drier.  Not a real worry.  The tank is made of steel, and you will be 6 feet under before that take blows apart due to rust.  

. So you really don't give a flying fluck by then.

Learn about HUMIDITY and how to keep it out of your paint(if that is your concern).  For spray painting cars, they don't use a 1 gallon tank.  More like a 20+ gallon tank with 3 compressor heads.

Just saying, too little information to go with as this is more a Hobby compressor.

Drain it frequently. You'll always have a moisture build up in an air compressor. Buy an in line moisture trap or filter if you are painting.

Don't use it..............

it has a drain plug. you open that and drain it