I haven't used Happy Camper, but Odorlos--which CW
just started carrying again has worked well for us as long as we've had the 2499. There is a big difference between maintaining a "clean" well functioning holding tank and rescuing a black tank that was abused in a seasonal site with the valve left open. Even walking around regular campgrounds it's rare not to see at least one or two RVs with both gray and black valves open.
We travel almost daily on our cross country trips and I dump both tanks every day. The fresh tank is securely attached with a steel cage. The black and gray tanks are attached with clips screwed into OSB and I tow as little as possible with as little as possible in them.
I know some people buy RVs to use all the facilities contained, but we came through tents and pop ups and still use the public facilities when acceptable.We don't put tp or garbage down the toilet or grease and all kinds of food prep solids down the sink. Our tanks dump clean even when 1/4 full and are flushed with at least one bucket of water plus one more to slosh around for travel. I occasionally use Odorlos because it has valve lubricant. Our sensors have always worked because there is no tp to gum them up. I have a Flush King, but only used it for the first year it took me to realize we didn't need it... and I don't have a wand to wave around in the toilet. This system is not for everyone, but has worked well for just two adults for years.
f you use your tanks heavily it is best to dump them as full as possible--it's a very simple concept of "head", just like a toilet tank is elevated above the bowl. Buy tp that dissolves in a day--test it in a bucket of water--and use something like Odorlos.