After finishing Alien Abduction, head to the Post Office building and go into the sewers. Use the alien probe to get further into the sewers and you'll come across a small house behind a gate. This is Mr. Hanky's house and he'll ask you to find his three kids.
Amber Hanky
From Mr. Hanky's house, go left and you should see Amber on a ledge with some sewage spewing down on her. Go up the nearby ladder and use the catwalk to go behind the sewage to your left. Turn the dial to shut it off, then go down the ladder and talk to Amber to save her.
Cornwalis Hanky
From where you saved Amber, climb the ladder again and use the catwalks to go all the way to the right. You should see another ladder going down, so take it and fight the two hobos and rats to save him.
Simon Hanky
You'll reach a spot in the sewers where you'll be in the background in the area with the defribrillator for the ManBearPig quest. Turn the dial here to lower the waste water, allowing you to freely return back to the surface now. Instead of going that way, go right and up the ladder you shoot down.
At the top of the ladder, go left and shoot the dial above the sewage pipe to make it go off and on. Break the board and go through the hole, then kill the rats to make their mother come out. Kill the Mama Rat in battle to rescue Simon.
Return to Mr. Hankey and you'll finish the quest, netting you two more friends (in addition to his children when you rescue them), as well as an item that lets you summon Mr. Hankey in battle.
