In the 2nd act of the game, you will need to make your way through a tunnel that is located inside of the washing machine of Lefty's back room.Make sure you DO NOT successfully go through this tunnel before unlocking this achievement. The achievement will be missed.
In order to go through this, Larry says that he needs directions. Go to Hell's Pawn on the map, and use the barred window at the bottom right to talk to Tuck.
"How do you manage to keep sneaking back in there?"
"You mean the part of your body where i found that cucumber?"
Tuck will give you the instructions, view it in your inventory. Then, head back to the washing machine. Use it.
"To the left, where the dead alligator is floating!"
"Straight ahead past the straw."
"... take the due and try to sneak past the troll!"
This will unlock your achievement.
Since it is necessary to go through the tunnel anyway, the actual solution is: