To freshen drains (not unclog them) and help keep them free flowing, mix 1/2 cup of baking soda and 1/4 cup table salt. Pour that down the drain and then add 1 cup of warm to hot vinegar. Let it foam and bubble for 15 minutes—longer does not work any better. Follow that by running hot tap water for at least 15 to 30 seconds. This is especially good for little-used drains, such as a guest bathroom.