i have found with many things that the way to get less fight is not to do it less, but to do it more. so my personal policy with hair washing, nail clipping, and now tooth brushing is to do it all the dam time, but maybe only a tiny bit each time. so we clip nails ever few days, but i only do an many figures as i can before the swimming starts. i wash hair nearly every night but maybe only for a moment and then rinse. i think it gets them into thinking it is really a tiny thing that just happens, rather than an event to fuss bout. now i am brushing teeth ever night, i sign the same song each time (ABC's) and ask them how far they can go? one is very ticklish in her mouth apparently, so it has turned into a contest of giggles to see you can get to the end of the sound for a big family cheer!
the other two things i did about water on the face, was from a tiny age i poured water over them, without soap and with my hand blocking most but not all from their face. we would always count 1,2,3 and pour, we started just pouring on their back and neck, then working up to the top of the head, in 4-5 pours each bath. they got so used to the counting, they know what to expect. i get a VERY dirty look if i forget to count now.
i also shower them and the play for a long time in the shower, so they are super used to water on their faces now, the stand under it and playa around, i'm actually very surprised.