I bought a big bottle of the Potty Toddy Tabs years ago when I had the Scamp with a 6-gallon black tank. I cut all of the tabs in half for that tank and they worked quite well.
I later had a TrailManor with a recirculating Airline-type toilet. I had to start using lots of the blue liquid to keep odors down. I still had a half bottle of the tabs. BTW: if anyone trys to sell you a recirculating toilet, run the other way, fast. They are a disaster!
I tried some of the liquid bacteria. It didn't work well on the recirculating toilet, but worked well in the Scamp.
Over the three years that I have had Airstreams, I have variously used either nothing at all or just one of the half-tabs in the tank. I have never had an odor problem in all that time except just one time when the toilet spring broke and the flush slide didn't seal properly. I do flush out the tank near the end of trips whenever possible to prevent any buildup.
John W. Irwin
2005 Classic 28 "Sabre-Dog III"
2013 Silverado 2500HD Duramax/Allison LTZ
WBCCI #9632, TAC TX-10