RE: Smaller vs Larger Portable Toilets
99% of the time I'm the only one using my portable toilet.  And I also
sometimes use it for gray water.  It will last three to five days of normal
camping (I have the smaller version that will slide under the bed).  It is
heavy enough to haul to a place to dump it, I'd not be happy with a larger
(and heavier) version.  So that weight when handling a full tank is a
consideration.