For the most part, black holding tank odors can be controlled through proper cleaning.
In most cases, plain old water will do the trick while in other cases a combination of water and a few basic ingredients will rid your bathroom of unwanted odors.
Before we begin to talk about how to get rid of odors, let's first discuss the workings of a black holding tank.
RV Black Tank 101: How does a black tank work?
The toilet in an RV sits directly above the tank, meaning any waste that falls from the toilet falls directly into the tank below and is held there until it is removed.
Here's where it gets a little personal.
Waste in its liquid form will disperse within the tank, but solids are not so easily moved.
If there is not enough water in your tank, the solids can form one large mass right underneath the pipe leading from the toilet to the tank.