Retired .. There are a couple of answers . It depends on your jug type . Less slack is best because some of those cats will roll themselves up in that extra slack . With a plastic jug, you can take up most of the slack . Now on a "flagging jug" type design jug with the rebarb , you have to account for the waves so they don't premature flag it so you may want 2-3 feet of slack .
I think that I have been doing mine around a foot or two . I really don't care if mine stand up vertical . I can see them easier and I can tell if they have a fish on them because they sit lower in the water and sometimes even bounce up and down .