RE: Potable Toilets
Well, I finally found the make/model of the toilet I've been using in my
Westy for 15 years now.  It's the SeaLand Sanipottie identical to the second
one shown on this page
http://www.sealandsanitation.com/portable_toilets.htm
the 2.8 gallon size.  It appears that that same item is marketed also by
Dometic and maybe even under other names.  One advantage is that I've run
into several sources on the Internet listing replacement parts for that
model and I know at least one person that did order and get a new pump for
one.
BTW, I didn't pay anywhere near those prices for mine about two years ago,
it was on sale at West Marine for well under $50.  The one I have now is a
replacement for the original bought about 1994.  After many years of use it
had developed a couple of minor problems and had become really groddy. When
I saw replacements on sale for that price I grabbed one. IIRC I'd paid about
$62 for the first one.
Now to check out in the Westy today for a brand name so I can respond to the
second thread on this subject about "What chemicals do you use?".