Teresa, I run the hot water faucet closest to the hot water heater. You may get a mixture of air and water, so wait for sustained water flow. If you are paranoid, you can loosen the drain plug on the side of the water heater to see if water comes out, but that would seem to defeat the purpose.
I have avoided buying one of those water totes—expensive and we've avoided being that full so far. But, I think eventually we will spend enough time in public campgrounds without sewer hookups and we will feel the necessity.
Complete boondocking—parked out on public land with no campground is where some people (no names please) open the grey water and liberate the tank.