Imagine trying to evenly thaw and heat a XXL rat under running water. It would never work. Now imagine doing this for 8 rats. No thank you.
I never warm my rats under running water. I place them all in a small tub and then add warm water. Once to thaw and then one water change to heat. So I'm not washing my rats and instead I'm soaking them in rat water. I then take the entire tub into the snake room and serve.
This method also helped me switch some from mice to rats by crossing the scents by soaking them together.
BTW, placing a large and XXL rat into a bag without putting a hole in it with their claws is pretty much impossible and I'm not cutting dead rats nails. So saying to put them in a bag that won't leak is much easier said than done.
In the end I found I didn't need bags. I've used my method for years with many snakes. It works for me and many other keepers. But I will agree that running the rats under water is not a good way to do things but then I never suggested doing that.