bought a parts washer from Harbor Freight. What is the best chemical to use for washing parts?

Bernie

I'm not sure if it's the best stuff but I have a friend that uses mineral spirits. Or call saftey clean. They have a program and will recycle your solvent.

Varsol (sp?), mineral spirits, paint thinner works good. They are all "almost" the same thing.

The trick is to also put about 12 liters of water (if this is a 20gal washer) in the washer. A lot of guys will say thats wrong... won't mix with a dino product, but thats the trick, the water sits at the bottom and collects all the crap, it's self cleaning.
Just make sure the water is well below the pump intake.

whatever you do don't use acetone in a parts washer. acetone is extremely flamable.

Chevron 321 solvent. It's the best commercial solvent that I've ever used and can be purchased at your friendly neighborhood chevron distribution outfit. I've tried all that tofu-solvent crap and it always left a scummy film on everything. I used Safety-Kleen services for a while and was never happy with the results. Also, they just got more and more expensive. I have a regular drain oil service come to my shop to pickup used motor oil and I just dump the used 321 in with the oil. They've never complained. Be sure to wear solvent-proof gloves when handling parts in any solvent.

Oops, I meant Chevron 325 solvent!!