parts washer fluid questions

Hi Y'all,

A good friend of mine just gave me a gently used parts washer. Jim is pushing 88 years of age, and is kinda done with the whole car thing. He said he used Naptha in it. I always heard to use mineral spirits, or varsol.

What do y'all use in one of these. I cant wait to fill it up and use it.

Thanks in advance
Matt