What should you do with your toilets when leaving for a lengthy time?

We are leaving our home for 6 months and was wondering what is suggested to with the toilets?
Should we empty the water out of the back or just add something to the water?

You should shut the valve off that's behind the toilet (it's just a little knob), then lift the seat and put a piece of plastic wrap over it. I forgot why, but I think it has something to do with bugs or something.