livewell help

[skipjake04]

If I am mounting a livewell under my leaning post and will have to run hose to drain, How much do I need to worry about overflow or draining.
If I use an already existing hole in transom for a pickup and drain using a thru hull, does it need to be at deck level.
I am asking this because I am not used to using "livewells" we normally just have an aerator in a baitwell.
It also looks on some of the rebuild threads that the thru hull drain is well above the deck, and my little brain can't understand how it would go uphill.
Is there enough presuure to push it like this. I would think the tank would just overflow.
any help would be appreciated
thanks
adam