Water pump plug?

Filled up the cooling system today following the engine rebuild. Once water got to the pump it came pouring out the back. There looks to be 2 outlets on the rear of the pump. One is already blocked the other just let the coolant flow out. What should be here? If so can I get a part number for a plug / screw?

Cheers.

It's a pre serp 3.9 efi if that makes a difference.

heater hose,some v8s use both other one,they use a core plug to seal them,154545

Great thanks. It's a to be used in a race car so no need for the heater!