How to operate the manual pump toilet

I have a 2000 242 fiesta vee and when I place the lever on the toilet to wet pump, (based of youtube video) it's supposed to pump water in the toilet while it also vacuums it out. The handle has a lot of back pressure and doesn't won't to go down. Is there a valve I have to open or am I doing something wrong and I don't know it?
Answers
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The toilet does not draw from your fresh water tank. It draws from the lake/river water. One thing that I do is flush the toilet dry. If I want water in it, I turn on the galley pump, then use water from the sink by pulling out the nozzle. It doesn't take a lot of water to flush. I never go number 2 on my boat either... Just my rule.
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Boat Name: King Kong
"Boat + Water = Fun"
There were 2 valves in the small opening on the steps. 1 of them did allow the toilet to flush but only when in the water, I assume as you all previously stated, because it pulls from the lake. I probably won't use the a/c much seeing since I currently do not have a slip at the marina yet, so do I need to open the seacock for the a/c? Also when I put the boat on the trailer, once I arrive home there is a small amount of flooding in the floor seems to be coming from that small opening that the valves are in. I did it before I ever opened the seacock for the toilet. Any know why there might be water pooling up in there and if so how might I get to stop?
Where is the strainer at and what does it look like? How do I know if one of the thru hull fittings are leaking?