This is inexpensive and probably safer to use on most dogs than the majority of commercial products out there, because it has no chemical additives. You can mix up a quart-size batch and put it in an empty shampoo bottle, or a gallon at a time and save it in a plastic milk jug.
1 pint liquid dishwashing soap (Ivory, Dawn, or Dove are gentle enough)
1 pint water
1 pint apple cider vinegar
4 oz. glycerine
4 oz. witch hazel
1 oz. tea tree oil
(The ingredients you don't have in your pantry are available at any pharmacy.)
Mix together, store in airtight bottles, and use as needed. This formula rinses out easily and leaves your dog's coat feeling shiny and soft.
How often should you bathe your dog? The new philosophy among holistic vets is to bathe the dog as often as necessary. Dirty skin is itchy skin. If your dog feels, looks, or smells dirty, bathe him. Some dogs need it twice a year. Others may need it twice a week.