Personally........
I fill fresh water tank and use my pump.
1) If pump occasionally 'burrups' then I know there is a minor leak/issue cause line pressure should not drop unless faucet/toilet/shower is used
2) Don't have to be concerned with CG water pressure issues
As for Waste tanks.......
I never leave any open cause sewer flies can come up into waste tank, set up home, have babies, invite cousins to join in.
Some will put a dip in sewer hose so that a water trap is made but I like dumping when tanks are FULL and that means having to remember at least a day ahead to close off grey dump valve.
I'm just not into all that remembering of stuff when out enjoying/relaxing with my trailer-----I like Simple.