We put food in the microwave and it should be cleaned with food!
All you need:
1- Half a cup of water (use a liquid measure cup)
2- Half a cup of white vinegar
3- Paper towel or a clean cloth towel
Mix the water and the vinegar in the container, put it in the microwave for 4 minutes; after the time is up, leave the cup inside the microwave for about 2 minutes, open it and wipe it clean with the paper towel or cloth. Toss the solution.
Note: Be careful with the 2 minutes time because most microwaves are made of plastic inside and the vinegar is very powerful and leavening longer can cause discoloration of some of the areas inside the microwave.