You can get medicine for ick that you put in the water from any pet store or even a place like WalMart. If you don't treat your fish when they get ick, they will die. It's a cheap fix to save them.
Anyway, I clean mine with dish soap when there won't be any fish in them after ward. Just wash it out, rinse well with hot water and leave it empty (and dry) until you need to use it again - if you want to use it right away, I'd recommend letting it sit out for a day or two to dry and then rinse again with hot water, fill it up, treat with ph balancer and let the water sit for a day or two. Then go ahead and add your fish.