How do you clean a toilet that has a year worth of rust stains?

this may help. I use the regular bowl cleaner to start with, then leaving that in the bowl, add industrial strength cleaner - about a large splash, then add ammonia - another splash, then scrub it with the toilet bowl brush for a few minutes, then let all that rest for several hours. I close the lid for any escaping fumes, but this does a wonder on any rust and residue. Best of luck...

In some instances the tank itself needs cleaning as well; maybe using something like baking soda.

If it is only rust or hard water, bleach will do. Pour it in and let it sit 5 min. Use a toilet brush then and flush. It really is that simple. If that doesn't do it, then there is another product. Go to the hardware, Lowe's, Home Depot, etc., and buy a product called C.L.R., and follow the directions. C.L.R. stands for calcium, lime, rust.

You can empty the bowl by dumping a full bucket of clean water into the bowl. From there I would suggest you use a pumic stone to scrub/rub away the hard water stains. Rust doesn't usually respond to bleach so if you have rust stains on the porcelain try a specific rust remover.

Flush the toilet and then pour a quarter cup of Borax into it. Use your toilet brush to swish it around. Next, add one to two cups of vinegar and let the mixture sit for 30 minutes. You should be able to scrub the stains away!