I bought a used parts washer, actually a "cuda" brand, I use powdered dish detergent, it gets the water near boiling, rotates the parts on a table and sprays the water and cleaner at high pressure on the part. Trans cases, heads or whatever come out nice and clean and ready to paint. I can pull a head for a head gasket, put it in the washer and go scrape the block off and when I am done with that the head is clean and ready to re-install unless it needs a little gasket scraping or milled. I completely quit useing the solvent one with a brush years ago and never looked back, they suck no matter what you use compared to a real parts washer. As for bolts, buts and other small parts I bought an amunition shell polisher from the local gun shop and throw em in with some diesel fuel and some BBs and after a little while in there they come out nice and clean. I have way better things to do than sit there scrubbing parts by hand.
I am not causing global warming, I am just trying to hold off a impending Ice Age!