Well...If you are not a commercial shop that gets serviced by "Safety Kleen" you can't use their cleaning solvent which is picked-up and recycled by their trucks. Most of the non-commercial "home" parts washers use a mineral spirits based solvent. Some market it as Stoddard Solvent. I get 5 gallon cans from "Motor Supply Company", but Tractor Supply I think has it too, they are just too far away from me which is why I don't go there.
The water based solvents are supposed to be used in a specially heated parts washer tank to be effective. These parts washers are REALLY expensive, but the water based solvents don't usually characterize as a hazardous waste.
On my parts washer which sits on a 30 gallon barrel, I have the solvent cycle through an oil filter that I attached to the back side of the tank with a remote filter housing. It does help extend the life of the solvent somewhat. I try to keep just enough solvent in the barrel to cover the pump. Keeping less than 5 gallons in most cases will exempt you from Federal regulations (just in case a disgruntled neighbor calls the local EPA on you).
Rono.
Ron Lane, Meridian, ID