The outlet on my westie is the same thread as a 'common' garden hose.  I
have used a cutoff female garden hose piece to feed a 1 gallon plastic jug.

IIRC some camping areas such as the Colorado River and Green River areas
near Moab UT REQUIRE full self containment including having a working
portapottie (thetford 135 works) and a closed greywater system.  Ideally
according to the NPS peace officer the greywater tank should be attached to
the vehicle.  (they let me off this time).  So...put a tee in the drain
after the trap and run a hose to a container inside the vehicle.  Meets the
letter of the law.

IIRC also the fine is pretty hefty.  NB these are the areas that aren't
fully supported camping areas where one finds clivus multrum and other such
fine composting devices.

Not likely youd' be cited on the Orinoco or the Columbia but who knows for
sure.  I'll doubledog betcha Lewis and Clark and Sacajawea didn't pack
theirs out but then the population pressure hadn't educated the bears back
then.

"wilderness is a place where the local residents can legally kill and eat
you"