I have been using the Blue Steak Chemical Dispenser Kit since it first came out about 17 years ago. Four RVs later, I have yet to find a product that even comes close. The Blue Streak is a reservoir that attaches to the RV wall behind the toilet and each time you flush a small amount of toilet chemical is dispensed into the toilet bowl and black water holding tank. It uses a specially designed T-Valve which draws the Blue Steak Chemical into the toilet when you flush.
Cut the toilet incoming flush hose and insert the valve between the cut. Place and tighten a clamp on each end.
Connect the hose from the Blue Streak Reservoir to the T-Valve. The T-Valve is a venturi that creates a vacuum to draw the chemical from the reservoir and mixes it with the water passing through the T-Valve.
The reservoir is mounted behind the toilet and filled with Blue Streak Chemical. The Blue Streak Chemical is a non-formaldehyde deodorant that contains detergent and a lubricant.
Flushing the toilet will draw a small amount of Blue Streak Chemical into the toilet. The chemical has light powder fragrance. Each flush draws in more chemical. No mess and no fuss, this has worked flawlessly for me for years.