How much liquid benadryl do you give a 12 pound dog?

I am a registered Vet assistant, and have been working at a vet clinic for some time. WE give liquid and pill form benadryl quite often to dogs. The rule of thumb is 1mg per pound. For example: a 25lb dog can take 25mg of benadryl.

I read on a veterinarian hospital page that you were NOT supposed to give the liquid form of benadryl to dogs.