How to prep aquarium water?

I have a 10-gallon tank with 2 crayfish and 5 fish that my dad caught in the river and decided to put into the tank (yes, this aquarium sounds a bit questionable, but bear with me). It's almost time for a water change. I know I'm supposed to use the gravel vacuum to clean the tank and remove the 10 - 15% water. But how do I go about replacing the water? Do I pour tap water in the tank, and immediately put the chlorine remover in (how would I estimate how much remover I put in? The instructions on the bottle only pertain to 10-gallons of water, not one or one-and-half-gallons (10-15%))? Do I just have a 10-gal bucket of pre-prepared water and use that over the weeks (I really don't have the storage or strength to keep and carry a 10-gal bucket of water every week)?