Many of the rafting supply stores sell a product call Knockout that is
made for this purpose. It is a liquid and you put in a very small
amount. It is a concentrated deodorant, and has worked pretty well on
our week long trips. It is fairly expensive, but lasts a long time
since you only use a little splash at a time.

Bill Tuthill wrote:
Maybe I should ask this on Boatertalk's rafting section,
but here goes.

Are any products useful to reduce portapotty odor?

I know of powdered Clorox (causes pressure build-up)
Blue Goo (never tried it, but some rafters swear by it)
and now Odorlos/Odørløs, a dry powder.