Welcome to the site
My family had a seasonal site in Ocean City, MD for many years.
The biggest mistake I saw people make was to leave the valve open on their Black tank since they had a sewer connection. You need to maintain a level of liquid in the tank to keep the solids from collecting in the tank and the volume of water when you open it to flush everything out. Of course, This was before we had flushing systems
We did leave our grey tank open all the time without any ill effects, but I saw many people with big time problems thinking the black tank could stay open.
I was nice when we upgraded to a Park Model that didn't have any tanks.
2004 Dodge Ram 2500 Club Cab 4x4 CTD
2007 Sunline Solaris T-276-SR: Misty Blue/Cherry
2001 Dodge Ram 1500 Reg Cab 4x4 OFF-ROAD