Fishing Boat Live Well Question?

[lifeshort]

I have a 1997 Starcraft Superfisherman boat with 3 live wells.
The two wells at the bow appear to run off the same 3 way rocker switch to fill water into the wells.
The well at the Stern also has a 3 way rocker switch.

If I press the stern switch up, water fills the well.
The middle setting on the switch if OFF.
What does the switch do when it is the bottom position?

Same question for the bow wells and switch.

The bow wells never appear to fully drain when the plugs are removed.
Could the rocker switch bottom position be something to help drain the water out of the wells, or is it just a recirculator
to give oxygen to the water?

Mine are 
pushed on top intermittent. Runs a while and shuts off, runs a while shuts off. To keep fish alive but not run continuous
Pushed center off
Pushed bottom run all the time

Water in your livewells is coming in from the lake