Residual water in black water tank

After emptying, I squirt a couple ounces of Dawn hand soap down the commode, flush a toilet bowl full of water, then call it done. The hand soap breaks up waste the same way it breaks up grease and food on dishes. It isn't perfect, but when I flush in the bathroom with the fan on, no stench comes out.

Water does evaporate in the black tank, so if one isn't using the rig in the summer, one might come back to a dry tank and "stone formations". The Dawn detergent helps with that, but it is wise to put enough water in to not risk chancing it.