Napa has solven in 5 gallon buckets for about $40 each. Dont worry about all the warnings on it, lol. I run that stuff in mine with water. From what Ive heard, once it sits, you can drain the water and the dirt/grim out the bottom and save most of the solvent usually. I havent tried it, I was just too cheap to spend more money on solvent, and the mix I have works good. Also, if you start having problems with it pumping or flow, make sure to check the filter on the pump box. Mine has gotten clogged up pretty bad before after some use.
~T.J.