Heather, you can put water into your deep fryer (drained of the oil) along with some dish detergent and let it heat up as if you were heating oil to fry something. Let it simmer for awhile to loosen any gunk. Dump out the water and scrub the inside. Use a plastic scrubber if it has a teflon or t-fal interior. If its just plain metal (stainless steel probably) you can scrub with soap filled steel wool pads. Then just rinse with clear water and dry and you're back in business!
I just cleaned mine using a paste of baking soda and water. I was amazed at how quickly the gunk came off! I have tried cleaning it several different ways over the past 2 years and nothing seemed to work. I prefer this method over trying Oven Cleaners and WD-40 since I don't know how they would react to foods.
I have tried dishwashing detergent and it took forever. Ours is a small industrial deep fryer. So when you take the baskets out it leaves oil on the sides and with teenagers all over the case.
Believe it or not my hubby is cleaning it right now. We could not find the cleaner and regular dish detergent would not work. He found out that Sunlight with oxy Dishwasher detergent would clean it fast and easy.
Dry, cooked on grease can be tough to remove and deep fryers can spatter a lot. This is a page about cleaning grease off a deep fryer.
Cleaning the baskets of a deep fryer can be challenging. This page is full of tips on how to clean deep fryer baskets.