Hello I have a 2020 Volante 329db The outdoor sink when running water with valve closed will fill up quickly and not drain unless you open the valve then it flows freely . Ran water in sink to see if it was also running to the back grey tank but it comes out only when black tank handle is open. Weird anyone else run into this?
Not unusual for a sink to drain into the black tank. It all depends on tank placement, if the black tank is closer or unable to run drain line to a grey tank properly.
It's also beneficial, no more water than that sink should drain, to add more water to the black tank. Water is your friend in the black tank to aid in draining better.