I know folks who get all upset over one grain of sand (and completly miss the concrete wall that is falling on top of them till it's too late).
This is a grain of sand issue.
First, "Mustard Gas" (Chlorine gas) has to reach a given concentration before it's dangerous. Now if you mix say a quart of bleach with a quart of ammonia, You are going to have a problem
When was the last time you used a quart of bleach on anything at one time?
NOTE: I have not done the research so I do not know what the minimum amount is to be dangerous.. But I do know it is more than I'd use at any one time and the black tank is vented to OUTSIDE the motor home.