We bought the smallest one at Lowes. It will hold about a gallon when it shuts off. It weigh a considerable bit because of compressor. It has a hose connection on the side under a cover. It can be set for continious or specific humidity level. It has good casters or wheels to move it about.
My first thought were to find one that sat on the counter. Didn't find one. Just set it in the shower with a short hose or run a hose to sinks.
It shouldn't fill gray tank in a long long time. I would set it on a ceramic surface or metal. I don't know too much about them but Lowes and others recalled some previous models becaue of fire.
If you look on the Net you will see the same models under GE and a variety, of names and prices. It has a filter, which we've yet to clean where all the air circulates through it. It pulls in a lot of air, obviously, to get the moisture out.