I use about a half cup of baking soda down each drain followed by around a cup of straight vinegar. Let it bubble and fizz around ten to fifteen minutes or until done fizzing. I follow this with a gallon of boiling water to rinse all this and the gunk down the drain. In the bathroom you need to get rid of the hair in the drains before doing anything. I use a zip it tool, it is a thin plastic stick with barbs on it made to remove hair from the drain and is real cheap. Remove as much hair as you can, then do the baking soda/vinegar/boiling water and they should be back to flowing well. If the drains are really gunky, it may take another round to get back to flowing really well. This should help you keep the drains flowing, Deborah, and it is a lot cheaper and safer than the chemicals you can buy. I have a plumbing friend and he has started doing this to his drains, it really keeps them clean!
baking soda and vinegar than hot water rinse