My tank is covered and I spray windex on the paper towel then walk over to clean the tank. No worry about contamination. I drop water when doing maintenance so need to windex to really get it clean.
I use a flipper for the inside. On the outside I used to use Windex but have switched to Invisible Glass. Just point it at a downward angle so the overspray doesn't get in the tank.
I use 1/4 vinegar and 3/4 RODI in a spray bottle. Cleans salt creep, finger prints, etc off the glass. Plus I don't have to worry about spray getting into the tank.