I researched this about a year ago for dish rags. Wound up using a microwave. 4 minutes is what is required to kill all germs; you soak it, wring it out so it's not dripping, put it in a corningware item ( I used a 2 cup glass measuring cup).

You'll see it start to boil. Keep an eye on it so it doesn't go dry.

And WATCH OUT... IT IS GOING TO BE HOT! use tongs to take it out of the cup.

Jeff