You can access this after getting the alien probe. Enter the sewers from the manhole outside the news office. Use the alien probe to beam yourself to the other side. Take the ladder down then shoot the valve to moderate the sewage flow. Go past it and operate the yellow valve to stop it completely. If you're still doing the sidequest “Manbearpig”, the generator there is where you'll have to place the Defilibrator.
Go around the corner and continue to the left. Pull the lever to access Mr. Hankey's home. After a scene, a new sidequest will become available. You can also pick up a Chinpokomon right outside Mr. Hankey's house.
Head further to the left to find one of Mr.Hanky's kids. Go up the ladder to reach the next area. In this area, go around the platform to the left and turn off the yellow valve. Go down the ladder and talk to Amber. She'll also be added to your friend list.
Climb back up then head to the right this time. Turn off the yellow valve then use the platform to go around. This will allow you to access the grate in the middle containing some items. Continue to the right but be careful of the waiting hobo. This is one of the seven homeless camps you need to clear out.
Continue further to the right and shoot the red valve. Go past the sewage pipe and you'll find two ladders going down. Destroy the wooden sheet to reveal a switch. Pulling the switch will lift the iron bars and will allow you to go up using the ladder. One of Jimbo's game targets are located here. (Penis Mouse)
After taking care of the Penis Mouse, climb down the ladder and use the ladder to the far right this time. In the area below, you'll find Cornwalis. Defeat the hobos to free him and update the objective. He'll be added to your friends list as well. Return to the previous area and backtrack. Go down the other ladder this time.
Head to the left and loot some items from the grate. Continue to the right and turn the yellow valve. This will lower the sewage level as well. Loot the chest to get a great weapon. Equip and modify it if you want then go along the walkway and continue east.
Defeat the hobos along the way then shoot the ladder beside the sewage pipe to lower it down. Climb up the ladder then head west. Go past the tunnel and shoot the red valve. Cross the pipe and destroy the wooden plank. Go through the hole in the wall and follow it to the left to reach Simon. You have to kill the rats around him but be careful since the mama rat will appear. Make sure you get a first strike since she'll engage you in battle with 5 other baby rates, making it dangerous if they act on the first turn.
You now have to return to Mr. Hanky to complete the quest. Since you're already deep here, just proceed to save yourself from multiple trips. Backtrack to the tunnel to the right and go up. Pull the lever then destroy the wooden plank along the way. Continue to the right and enter the tunnel there.
In the next screen, pull the lever to create a walkway. Now shoot the red valve to the right. Loot the items there then go down the ladder. Head to the left and be careful of the hobo ambush. This is also counted towards the seven homeless camps relocated.
Pull the lever to the left then head north. Turn the yellow valve and loot the grate along the way. Enter the tunnel then head to the left. Go past the sewage pipe then enter another tunnel. From there, you can go down the ladder to reach the cavern with a crab person. Just go past it for the meantime and continue to the far right. Once you've reached the ladder, take the lower path and place the bait there to summon the Fruit Bat. After defeating it, you can climb up the ladder to open up an alternate entrance near the cinema.
Finally, talk to Mr. Hanky to complete the quest and receive your rewards.
- New Friend Requests: Mr. Hankey, Mrs. Hankey
- Summon Item: Piece of Poo