Well actually, I've been pretty good with drywall but working with it at the department store and in my mother's house, I wonder how anyone could stand to do it for a living. Then I asked my cousin David who has several rental properties and he says professional drywallers are "All a bunch of drunks" and so that is how they cope with it. As for the drains, I have a hint. When a kitchen sink drain is clogged, I have had better luck with drain cleaners if you do the following: Get a big bucket, and place under the trap. Undo the trap and remove it, there will be a lot of dirty water in the bucket that you will have to dispose of somewhere else. If you already used a drain cleaner be sure to wear sturdy rubber gloves, old clothes and eye protection. The trap is in the form of a P and loosen the elbow that goes into the wall. Turn this elbow, which normally points down, upward and retighten. Then pour the product into the upturned elbow. I find that this works every time! You will have to reassemble the plumbing and it is messier, but like I said it really does work.
Pulsator, I feel bad over what happened with your plumbing, it is possible you may need a new sewer line. This happened in our neighborhood too.