You can actually buy cleaning solvent at most autoparts stores for a pretty big price.
I use Kerosene because it works at least as well as any other solvent and it's cheaper. (Use gloves though, all the petro solvents will be absorbed thru your skin).
After I get it too dirty to use I then filter it thru a rag or other suitable filter and burn it (along with all of my and my neighbors waste oil) in my Lanair waste oil furnace. http://www.lanair.com/home.cfm
