First, clean your drains thoroughly - get rid of all the black gunk by using the new zipit tool available at local stores or any device that gets out the big chunks.  Then mix a 5 to 1 water/bleach solution and flush the drains, followed by copious amounts of boiling water - at least 4 cups.  Then the next day, start  by dumping 1/2 cup of salt down the drain.  Then dump 1/2 cup of baking soda down on top of it.  Follow that with 1 cup of plain white vinegar and let the fun begin!  Allow all of this to set overnight, and flush it all down with at least 2 cups of boiling water in the morning.  To prevent future infestations, clean your drains often with this same solution.