There are, but only one I recommend
The cartridge inline devices do perform as advertised--to a point: the mfrs claim they reduce or eliminate intake odors AND eliminate the need for an additional holding tank treatment . The first claim is true--the do eliminate intake odors (some better than others), but they don't replace a holding tank treatment. The chemicals in 'em aren't compatible with K.O. or Odorlos in the holding tank, and they can damage the electrodes in a Lectra/San. There are only two solutions to the problem that I recommend. The simplest and least expensive is described in the article "Intake Odor Cure" in the HM Library...the other is a Raritan "Toilet Water Kit," which consists of a 2 liter bottle filled with a 1-3 mixture of Raritan "C.P" (bio-enzymatic bowl cleaner that destroys odor on contact) and water...a 1/4" hose connects it to the elbow on the back of the bowl, and each flush siphons a bit out of the bottle. All the major boat supply stores carry the Toilet Water Kit, about $30.
