pull knob on passenger side

I have a 1986 Procraft 1950V, the boat has a knob on the passenger side that can be pulled out or pushed in. The previous owner told me to pull the knob out and it would allow water to enter into the livewells, however the first time I put the boat in the water the livewells filled up even though the knob was still pushed in. Can anyone provide information on what the knob actually is and what it does. There is two hose at the back of the boat, he said one drew water in and the other was an exit hose.