to get the detective you must investigat the facility and to get human plug you must hold the flow on the caverns ok.
Those're pretty lame tips. I mean, those're the hints given to you in-game.
When he said detective, he means you'll have to do some, "investigating". Go to Level 5, but don't go in the vent yet. Go to the black part of the map, and crouch. Walk through and you'll land on a room. Inside it is a dead body. So, the word, "Detective" derives from it.
For human plug, play any Caverns match. Stand on the fountain of water for around five seconds. By then, you would've received a medal for being a, "human plug" and, "holding the flow".
