As mentioned... water is your friend. Chemicals are not.
What I do is when ever I travel, I first make sure the tank is empty and then I put about 5 gallons of water in it. I then put a cup of liquid laundry detergent (I use Oxy-Clean) and a 1/2 cup of Calvin water softener and then hit the road. While driving, the solution will slosh around the inside of the tank and will loosen (and or soften) solids through out the tank. Upon arriving at my destination for the day, I then fill then tank with water and then dump.
This procedure has worked for me for all my rv's to keep them free of sticking solids, no odors, free flowing dumping and as a n added benefit, keeps the level sensors working properly.
I've heard nothing but good reviews about Happy Camper, but I think the extra cost is not worth it since I get the same (if not better) results from soap and water.
Good luck and I hope this helps
Ron