I got to thinking about this the other day, this friend of mine asked me to help him unclog the drain coming out of his kitchen sink. It was something that I could not really help him with. I had a snake (they call it an auger some places) and I helped him take the p trap out so that we could clean out the pipes. However I could not get to the clog, it was too far down in the pipes. I have heard of things called sani sticks that are supposed to prevent this sort of thing, but I guess that the real thing is to never really put things down the drain. For example I guess that you should always let the grease in your skillets cool down and then put it in the trash. I know this one guy who puts bacon grease on things like toilet paper rolls, then he uses that to start fires in his fireplace. It makes the entire house smell like bacon.
At any rate the best way to avoid clogs is obviously not to get too much stuff in the drain, but that is really tough when you have small children. You teach them to put their dishes in the sink, but that is not enough. You have to get the food out of them before you do that. It is a big thing for you to think about, since this was really expensive. It took the plumber about two hours to fix this, they had to crawl under the house and cut out a piece of pipe about twelve feet long. There was a huge clog in it and they were not sure that the pipe was still good after they finished. Cast iron is not going to last for an infinite time under these circumstances.