I agree with Claire's advice..we have metal screens on the kitchen sink drain, the bathroom sink drain and even the shower drain. This is even when I never wash my hair in the casita...I do it outside, the Army way, or in the campground bathroom...and my husband is bald and has a beard.
So we don't have hair clogging up the drains. We have had our casita for 8 years and have never had a clog, and I don't foresee it happening.
But there are times when we do dishes inside, and the screens work for that, as well. NEVER, as Bob K4TAX and others have advised, put something down the sink drain that isn't water or straight liquid, or, what was so civilly put, digested by your body into the toilet. Meal scraps, leftover bits of scrambled egg, uneaten dog food, that bit of toast, coffee grounds...etc, all go into the trash. In fact, when I do do dishes inside, I use a dish pan and then dump that into the campground dishwater dump, if they have one. Most do.
Please, if you've not damaged the pipes or tank after using sulfuric acid, you lucked out. Don't put anything like sulfuric acid down the drain again. Not even the stuff called 'drain cleaner." IF and this is a big IF..you have a blockage of that sort in the tanks, white vinegar should help, or the liquid made specifically for "RV toilets" and some folks swear by using Calgon water softener to break up the big chunks.
Not only is sulfuric acid dangerous, as in some scenarios posted by others on this thread, but by dumping it into a municipal, or a campground dumpsite, you have violated the regulations and, possibly, even the law. By dumping a chemical that has no business being used as drain cleaner, you have possibly endangered the poor souls who have to pump the tanks out. Sulfuric acid belongs in car batteries, not gray or blackwater tanks.