Thanks to everyone who responded. Your replies are appreciated!
I think that the odor problem I discussed in the original post is due to the fact that we "dry camp" a lot as opposed to camping in RV parks. As such, our dumping is less frequent. And, as I mentioned, the summer here has been the hottest on record. Even as we approach the official start of autumn, it's still very hot.
I found a Canadian-made product that I'll be trying soon. I am impressed with their statement: "The naturally derived ingredients are unaffected by hot weather and heavy use and do not lose strength over time. RVM is readily biodegradable, contains no chemicals, bacteria or fragrances. RVM can be safely discharged to dumping stations."
HERE is the link to this product. After I'm able to rinse the tanks and try this treatment, I'll report the results.
Home Depot in Canada sells the product on-line for $10.99 Canadian for a 1 L bottle.
The GEO method is OK, IMHO, for those who are able to dump more frequently and have lots of water available. Given the type of "camping" we do, we're not in that category.