are many brands and kinds of holding tank chemicals all claiming
to control odor and dissolve solids. Except for avoiding
those containing formaldehyde or similar take your pick.
I have even used liquid laundry detergent with fair results.
RVers are recommending enzyme-based chemicals which use live
bacteria to breakdown and digest the odor causing waste.
We've tried these and they do seem to work. I've had fair
results with TST brand from Camco but
so far but I'll use any chemical that's on sale. I have a
thing against putting money down a black hole.
don't think there is any difference between the liquid and
dry as far as how they work. We like the dry packets just
because they store better but they also create dust when
poured which we don't like to breathe.
the last year or so I've been using OdoBan that I get at
Sams Club. It's a potent liquid that really does eliminate
the odor provided you start with a clean tank.
you need to add chemicals to the black-water tank after each
dump. Same for the gray-water tank although I don't feel
it is as important.
you have drained and rinsed the black-water tank, close the
valve and add enough fresh water to cover the bottom about
an inch deep. Then add the chemicals. I like to add the chemicals
a little at a time as I 'flush' the toilet. I think it helps
disburse the chemicals.
we're hooked up to park services, we leave our gray water
tank valve open. When we're 'hooked up', for and extended
time... several weeks... I like to close the gray water valve,
add some chemical to the tank, and let it fill up. I do this
about once a week. I seems to keep the tank from getting
sour... which can be almost as bad a smell as the black tank!