Take it out, add hot water and a little liquid dish soap...throw in a handfull of fish aquarium rock or something simular, then shake rattle and roll upside down and all around, empty and RINSE good several times and you will be done with that job in about 10 minutes.
Once the gunk is out, fill it with powdered dishwashing detergent and water, mix well, then leave it sit overnight. Inside should be spotless come morning. Using the rocks is a great idea to get the stuff out before you do this.
Note I haven't done this myself - just heard of it.
Try getting one of those sponge on a stick thingys in there to scrub it. I doubt there is any sort of solvent that will get it clean without scrubbing the inside of it. Maybe even a stiff paint brush may work too.
I wonder if a dishwasher could help, but the jets wont be able to really get in there and spray, but the hot soapy water just might work. I have also sprayed brake cleaner and carb cleaner with the red nozzle attached and got them fairly clean too.
Okay, I got it clean. Thanks for all the interest.
I used a mix of soapy water and CLR. I threw in a handful of nuts, screws small nails and washers (I didn't have an rocks). Swirled around for about 10 minutes and it came out pretty clean. Not perfect, but really pretty good.
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