We use our toilet for liquids only and also camp in the middle of Winter when the TT is already winterized.
In the Winter I pour about a half gallon of pink anti-freeze down the toilet prior to leaving the house and then we have a small plastic bottle that we fill with water and use to flush the toilet with - works great. There's no reason that same principle (minus the anti-freeze) couldn't be used in the summer.
On our lightweight TT we can't afford to travel around with a full tank of fresh water due to GVWR, so if we dry camp we bring along water in collapsible jugs loaded in our TV.