Mineral spirits here.
Stoddard Solvent (fuzzy memory right now... insufficient caffeine ingestion this AM) is recommended for parts washers, but it's nothing more than mineral spirits with an additive to raise the flash point. I think this is what Safety Clean uses or did use.
I made my parts washer out of a 55 gal drum cut in half and a 20 gal drum for the spirits. Near the top of the 20 gal drum I welded in some tabs to support a metal screen on top of which I threw some old rags to help filter out the bigger chunks. Periodically I throw the dirty rags out on the driveway to dry out and then toss.
About a year ago, the chemical manufactures decided to create a new product called Paint Thinner that was not 100% mineral spirits. They then offered two products; Mineral Spirits and Paint Thinner, the thinner having an oily residue compared to spirits. It was a shot at trying to jack the price of spirits. It apparently didn't work as I see paint thinner is back to being 100% spirits, but still spendy.