don't wash them in cold water..
i wash my guys in the tub..one is a dalmatian puppy and the other is a mixed breed.. they are both arounnd 40 pounds, they won't get in the tub on their own..but after i get them in there they are fine.. i never tried the waterless shampoos, but i had a friend that did,and she said they work just fine...
if you just clean out the tub afterwards, i see no problem with washing them in there...