Cleaning muffin tins can be a nightmare. They get all crusty and stuck on after doing a few batches. I used to fill them with hot water and let them soak in the sink for hours, but they took up the whole sink! I now have an amazingly fast and easy solution. 
Step 1: Fill muffin tin with water.
I fill each muffin hole about 2/3 full.
Step 2: Place into oven.
I turn off my oven once my last batch of muffins in done. After removing the last batch of muffins, I immediately fill my muffin tin with water, while it is still hot, and place into the hot oven.
Step 3: Cook in oven.
I leave in the oven for 8-10 minutes. Note: Set a timer or you will forget.
Step 4: Dump and Clean.
Remove from the oven and dump the very hot water out. Wipe away the softened crust with a brush or cloth and rinse. Now you have a perfectly clean muffin tin without any “elbow grease” and without soaking a large pan in your sink for hours!
Note: Mine is clean, it just has several scratches and is discoloring over time.