How long will 26 gallons last? (Also, a power question.)

Thank you :) For the record, we should have 40 gallons of fresh water and access to more but it probably won't be a hose connection so maybe that's not useful; we won't be cooking with it or drinking it, so it's mostly for washing up a little and the toilet. I think we'll be OK in the fresh water department.

Is it usually possible to pour fresh water into the tank somehow? Or does it require a hose hookup to fill?

Thanks again - it's going to be fun & a big learning experience :)