while in the water the seacock is always open , it should not leak or let water in, if it does thats a problem, you can close it but your livewell wont work, mine is always open and I have no problems.
I had a similar problem last year - a slow leak where my batteries would drain after about a week from pumping. I found the problem by filling up the bilge while on the trailer. I only had to put a few gallons in and I noticed that water was seeping from behind my fish finder transducer. Upon removing it I found an extra hole that had been drilled and not filled properly.
while in the water the seacock is always open , it should not leak or let water in, if it does thats a problem, you can close it but your livewell wont work, mine is always open and I have no problems.
Same with me. Always open and never had any reverse seepage.