How do you prime a jet-pump

At the top of the pump housing you will find a plug (might be a pressure gauge). Remove plug... fill with water until it overflows... replace plug.

Spot on with the answer. Let me add a bit. The impeller cage will fill to the top If the water drains away and you have to keep adding water then you have a faulty check valve that must be replaced before the pump will hold prime. Good luck, Tom

So if you have to keep pulling the plug and adding water the foot valve is bad?