You need to plumb it off the a tee in the line from the pump to the tank. There must be no shutoff valves that could ever be closed to isolate the relief valve from the tank or the pump.
The valve must be sized to protect the tank. Most tanks will handle more than 100 psi and many pumps will exceed that at shutoff (low flow).
Determine the flow of the pump at the rated tank pressure. The valve must be large enough to discharge the flow of the pump at the safe pressure of the tank. A preset 75 psi, 3/4" valve will discharge a lot of water. If you need to pipe it anywhere the pipe should not have any thread on the end. A 3/4" Watts 530C costs about $20 at Grainger. I couldn't find the flow rating right now but I'm sure it's available.