Best time to empty black water tank

Thanks all y'all for your input on my questions. I guess I've been doing it right, though I normally leave the grey water tank open all the time. All my sinks have traps so I'm not getting any odors. That idea about putting a loop to create a trap in your main drain makes a lot of sense. I may try it if I have future odor problems. So far I'm just parked and will be until November when I'm driving out to Tucson for the holidays, as well as quail hunting (and eating, YUM!) with my dog.
Steve