I use a 25 gallon tote and tow it behind my truck...nice and slow. Most of the time, I only use it for gray water when I don't have full hook-ups. But, using it for emptying the black tank isn't a problem. I monitor the filling process very carefully and only fill it about 3/4 full.
As others stated, use campground facilities to avoid filling black tank too quickly. By doing that, you should be able to do 2-3 days before filling the black tank. If you have kids, make sure they understand to flush with minimum amount of water.