40 gal grey tank owner here. I have a 32 gal Barker 2 wheel tote and the long extendable handle gives enough leverage to move it around when full. It's towed by the truck anyway so I don't care much about the weight. If you go larger, go with a 4 wheel model. As to the small 18 gal totes, that wouldn't work for me.
BTW, I bought the optional float thingy that goes in the top and found it kind of useless. I either threw it in my tool box or threw it away, don't remember. If you pay attention, you can easily shut the valve off before it overflows.