Civic leaking connecting pipe, help!

[Nathfest]

I recently replaced the engine in my '97 Civic after doing a mini-me swap. I just recently got the engine running, but after running several minutes it started leaking rapidly from the pipe in the back of the engine, from the stem right next to the water pump. I need to know what this is, I'm not sure if a hose is supposed to go there or do I need a new water pump?