We have a 32 gallon grey tank. We have two 15 gallon Barker blue totes. The smaller size totes are (barely) light enough to lift into the truck when full. The dump stations at most of the places we camp are very far from the sites and putting them into the bed is the best option for us. Having two lets us accumulate more before we have to make the run without dealing with a single tank that is too heavy to handle the way we need to. Typically, we are only using the totes for grey water, so if we accidentally overflow it isn't the end of the world.