First off get a tank equal to or larger than your largest tank. Then
get one of these to put on where your sewer hose connects (valve connects between camper sewer outlet, sewer hose connects to this valve.
I have about 6 ft. of pipe between the tank dump valve and the fitting the sewer hose connects. you'll only make the mistake once on how full you tote is, before you buy the valve. My 3 tanks are 45 gallon each. I was lucky I was dumping a gray tank, when I figured it out.
I have the Barker 42 gallon tote, and have added the pneumatic 10" HF tires also, and would not buy any other tank than a Barker. We volunteer at a State Park for the summer and have seen several of the 3 wheeled totes that have had the front wheel push in and crack the bottom of the tank. You can guess what kind of mess that makes. The small front wheel assembly with a thin walled tank going down the road hits a crack or rock, the bottom fails and ??? hits the road.
Buy a Barker you'll never regret it.
Just FYI, I replaced the wheels because I wore the original tires out, after two years. I'm parked for 6 months or more at the S.P. and don't want to move it every time I need to dump tanks.