Try inexpensive denture cleaning tablets maybe get a couple from your dentist they get lots of free samples. I used to work for a dentist for 17 years and those tablets cleaned quite a bit. I used to use them to soak office coffee pot that no one would wash though all used it.
I also use the dryer sheet trick. I don't even have to use a whole one; I use half a sheet for a larger baking dishes and a quarter of a sheet for smaller dishes. Drop the sheet in and fill with hot water. (I haven't tried it, but moistened dryer sheets are also supposed to be good for getting the soap scum off of glass shower doors.)
If I ever have cooked on food I use a dryer sheet. Just put the dryer sheet in the bottom & run hot water over it making sure that the water level covers the food & let it sit for an hour or so. Then just wipe the food off with the dryer sheet. Works everytime & I never scrub my cassorole dishes thanks to this little tip.
I have had this happen and my crock pot is white. I filled it with boiling water and bleach. I let it set for a couple of hours and it helped. I then washed it and rinsed, rinsed, rinsed, completely. I did find some liners by Reynolds Wrap that I now use for the crock pot. These are amazing and work great.
This is what I do; I fill the pot with hot water, add a 1/4 cup dish washing soap, bring it to a simmer, and then put a lid on it so it stays hot after I turn it off. Leave it for a few hours. The food came right off. If there is a little residue I put some cleanser on a dishcloth and scrub on it lightly and it comes off. (06/25/2009)
It might be best to avoid SOS or similar scouring pads because they can create tiny scratches that may make it even harder to clean your appliance. The hot water soak (even without soap added) is very effective. I fill the crock to max fill level with hot water, drape 3 - 4 clean dry face cloths on lid to cover lid entirely, and leave it unplugged and let soak a few hours. The facecloth (or even a folded towel) help maintain the warmth which increases the effectiveness. (06/25/2009)
I use a cleaner called Cameo. They make one for porcelain, for stainless steel and aluminum. You sprinkle some on the cooked on food and use a damp cloth to make it into a paste. Then you rub it on the spots and they should come off with a little bit of elbow grease. I buy mine at Walmart in the cleaning aisle for about $1. I have heard you can make a paste with baking soda and clean just about anything. Although I have not tried this myself, it might just save you a trip to the store! (06/25/2009)
Use one of the Magic Erasers - I think Mr. Clean makes them. They clean everything off my pots and pans and they are soft and don't scratch. Stuff comes off immediately with little effort. We even cleaned the vinyl car seats and doors in my husband's car and it looks showroom new (it's a 2001 model!). We've used them to clean the water line in our pool, our glass top stove, etc. I love them! (06/25/2009)
Once clean, can I suggest that they make crock pot liners? They sell them with the plastic wrap and aluminum foil where I am at. I love them. Just pop one in, then whatever you are cooking and when done take out and throw away. They have saved me time and trouble. (06/25/2009)
Next time you use your crock pot, use this little trick someone told my mother many moons ago. Using a pastry brush or a folded up piece of paper towel, oil the whole inside of the pot, top to bottom. Although it will still need some scrubbing to clean up, it will be easier to maintain. I've been doing this for years with extra virgin olive oil, but any liquid oil will do. (06/30/2009)