When we get to a campsite, we don't even hook up the sewer until we need it.
Note: We don't haul a toad, and we are quick to drive our RV into town or to some nearby destination. Of course we are never in one spot more than 3 days, or I will go crazy.
I connect only when / if the gray gets to 2/3rds. Our Bathroom sink flows to the gray which originally I thought I hated, but over time I have learned it works to perfection the way we use. Our Gray ALWAYS fills before our Black. When I do hook up sewer, it is to dump the Black tank first whatever it may have ( I don't check the level), and then followed by the Gray which is at least 2/3rds. I over do the Sani Flush when at a campsite sewer hook up
I try to have both empty when we leave if for no other reason to reduce the weight to give me more power to pass trucks.