yeah, what Kathryn said is correct.
You need a gate valve where the main drain pipe enters the sump and the pipe beyond that valve should extend below the surface of the sump water only a little bit to allow all of the air to get out of the line when the pump starts up. Ball valve is easier to get at Lowes or Home Depot, but you won't like trying to slightly adjust it to get the water level in the external box correct.