That's pretty much what I did with mine. I used 2 gallons and used the freshwater pump to pump it through the faucets and into the drains.
My air compressor is in my garage, so getting air to the city water fitting was easy with this:
http://www.amazon.com/Camco-36143-Brass-Quick-Connect/dp/B002XL2IEA/ref=sr_1_1?ie=UTF8&qid=1417357020&sr=8-1&keywords=camco+air+water+fittingI used 25 psi. My air compressor has a regulator since I use it for air tools. Unrelated - what sorts of things do you use air compressors for that they don't have a pressure regulator on them? Seems odd to me.
It took me a little while to figure out the bypass procedure for the hot water tank because one of the valves was "hidden" but I eventually found it.