Water treatment when hooked up to sewer

I hope you do not keep the blackwater drain open. Sometimes in the summer hot months, we do use the pods, they do help keep extra odors down, until we do dump the tank. Usually can go several days between dumps. The greywater valve does stay open, as we have a flush line to the black tank. I usually close the greywater valve a few days before final leaving, just to give an extra flush to the drain line before detaching it. But to answer your question, NO, it is not really necessary in most cases.