Hot tank

Degreaser and pressure washer worked for me. Bit of work and quite messy.... First scrape and heavy gunk off. Then spray with engined egreaser. Brush it in good Scrub and rinse till nothing left. But as you mention boiling -I think hot water is key to doing a good cleaning job. I don't have hot water hookup outside, so layed long coil of garden hose in the sun (back in mid-summer) feeding the pressure washer. Got about 1 minutes worth of really hot water every 10 minutes or so LOL
I guess small stuff could be done in a dishwasher, but not sure what you might use to handle a block to do it 'automatically"