You make a supply hose and plug in your log splitter and run the OUT hose to tank.
If your hyd system is open center, the pump flow passes through all valves in series and your log splitter will be in series with the pump flow.
Now as to where you get the pump flow might be directly from the pump, or the FEL if you have one, or even a remote valve.
Your tractor hyd pump and engine rpm will determine the flow as to the GPM's delivered to the log splitter.