[Bryan A.]

Wart - What is the second ball valve for? I assume you have them t'd together somehow and open the valve to allow the old tank to fill, where does the second valve come in? Just wondering. I am doing exactly what you did only on a smaller scale, I am connecting them to my makeshift manifold with quick connectors and flexible hose because the two compressors are portable.

abl1111 - The short answer is the biggest you can afford. From what I gather you are basically looking at HP of the motor, capacity in gallons of the tank, Max PSI and most important CFM or cubic feet per minute. I am sure others will add to my list.