[PonchoV8]

My house is 40 yrs old and I'm on city sewer--galvanized and cast iron vent and drains. I have a couple of drains that are just slow. Plunging doesn't yield any good results. I got the master bath sink to clean up finally by copious plunging, but the tub will not plunge free. I think it suffers from a buildup of black slime like the sink did, but I can't maintain good suction with the plunger to get it to run freely.

What treatments can I run through the plumbing that will make sure it's clean. I'd like to keep the sink clean too instead of plunging it every month.