Hmm,
Just odd for dog fleas to be feeding on rat. See if you can get some xeno, do NOT use dog flea treatments on your rat, far too strong, or phone your vet.
If you are going to bathe them, fill the sink bowl with very luke warm water.
Put a towel at the side of the sink.
Put a small bit of the small animal shampoo (makes sure it is ok and not use on rats under 300g) lather in your hands and rub onto the ratty while he is on the towel. Get in the creases and warm spots, behind neck, ears, under arms and thighs.
To rinse him:
You then need to put your ratty on his belly and with your left hand place it flat over your rattys head and fingers under his forearms, then with your other hand on his back end fingers under his legs. Almost like how you would hold a rail in front of you. This should stop wriggling, biting and most importantly not get water in their ears.
Turn your rat over and gently swish him back and forward in the water, do not dunk him totally, swish his belly in, but keep this process going until he has the shampoo off.
You could also try "buddah" your ratty where you sit him on his bum with his tail in front and hold under his arms quite high up. He shouldnt be able to move much but its the wetter variation!
Put them on a towel in a carrier and let them dry, dont put them in the cage wet, I put mine on the sofa with me and a big towel and they all snuggle under until puffballs.
They will temp hate you but worth it. Take your time and you should come out all less stressed
x