i count out how many rats i need and put them in a ziplock freezer bag. then i let them sit for several hours to thaw. i fill a tub with hot water and place the bag-o-rats in it and weigh them down with a heavy bowl so that they stay completely submerged. i generally have to dump the water and add more hot water once or twice during the process depending on how thawed they were to start, but i also thaw 8-10+ rats at a time so it takes a bit longer.
now here is a way NOT to thaw your rats. last week our hot water heater broke and it took a few days for maintenace to come and get it fixed (wow, cold showers hurt in the morning!). i got the bright idea to heat my rodents on the stove as the microwave is a BIG no. so i did the same thawing for a few hours in the ziplock bag deal and then put the bag into a big pot of water on the stove. i let that heat for a while until the rats all seemed nice and thawed and evenly heated. now, my first mistake here was heating the rats up too quickly, so i had several exploded bellies. messy, but nice for scenting the herp room. my second mistake was that stoves are made for COOKING THINGS! i attempted to pick up the first rat and its tail broke right off--nice and tender, cooked all the way through. yuck. needless to say, the snakes did not get fed that night. the next morning i called the apt. office and freaked out on them and we now have nice hot water from the tub to warm the ratties in.