Ah, and those that say they never have smells and no need to clean their tanks or rinse them out, well ... here ya go! If they didn't stink, then why all the chemicals, flushing and everything else that's done to keep smells at bay?
Seals in the toilet do not stop all the smells. Once the peddle on the toilet is pushed, odors and smells can (and do) come back up the hole if the tank itself is filled with nasties that have been sitting a while.
The ONLY solution to ridding the tank of smells is to clean it out. Any process you can do to accomplish that is what's needed. Clean tanks don't smell, unless the contents sit for a length of time. And the longer that time, the more prone to foul smells.
As said, cleaning the tank is the only way to get rid of the smells. Over time stuff sticks to the bottom, the sides, and even the top of the tank. If you have solids and liquids in the tank and you hit the road, the contents inside that tank are splashing everywhere, including the top of the tank. Well, each splash is leaving "stuff" on the top of the tank and the water drips off. Over time, again and again and again, it builds up. Never getting clean off ... yea ... it stinks (literally).
The solution, again, for eliminating odors, is to clean the tank.
Start by filing it completely. Fill water into the tank until it actually comes up into the toilet (above the neck). Look down the hole and watch for the water to reach the neck of the toilet. Yea ... the toilet seals on the floor better be pretty secure for this. You will know how well sealed the toilet is to the floor this way too (which is a possible place of escape for smells too).
Dump the contents after letting it soak a few minutes. This gets water on the TOP of the tank, as well as sides and bottom.
After dumping, use your black tank flusher and rinse the dickins out of the tank. If you don't have a built in rinser, then get a toilet wand and attach to a garden hose and shove it down the toilet and rinse the dickens out of the tank. The force of the spray will help break up anything stuck, top, bottom, and sides. Make sure you are dumping as you rinse.
Rinse, rinse, rinse.... use a clear section of drain pipe on our camper sewer outlet so you can see what's REALLY coming out. When it runs clean, you've finally got it.
Then another thing you can do it add about 5 gallons of clean water, a few squirts of Dawn Dishwashig liquid and go for a nice drive. The bouncing and turning of the camper will slosh that soap water around and clean even more. You can add bleach too, which really help freshen things up.
Once back home (or your campsite), drain right away so all the gunk comes one. If you use the clear section on the drain again, you'll be absolutely shocked how nasty the stuff is coming out of the tank.
I promise you, if you do this, you'll not have any more smells. Rinse, rinse, rinse.
Then, every time you hit the road, make sure your tanks are dumped, add a few gallons of water and bit of Dawn and go to your next destination. You will NEVER have smells and you won't have to use chemicals either.
