The "vent" does not apply to the waste pipe in the water by the Carrot Cake Factory. You enter the factory there by using the crowbar.
The "vent system" is a maze of ducts that leads to various rooms inside the factory. (Printing, Processing, and Freezer) To enter the system you first need the blueprint, which is on the roof of the factory in a boarded window.
To leave the factory : use the Carrot Transporter.
To reach the vents : You can get from the engine room to the vent system (and other rooms) by starting up the large overhead crane. The power controls at the left turn on the lights and the crane. Push the outside two buttons halfway down, and the middle one all the way down. Now you can climb up the boxes at right, to reach the upper left, and LEAP onto the moving crane as it gets close. It will carry you to other side and the vent entrance. All three of the interior rooms are connected by the vent system (the map was outside the factory on the upper window).
Chat with our AI personalities
The blueprint to the vent system is on top of the factory in the boarded window. The Printing room is along the right side. You can get the secret password there, once you free the drone from his mind-control rabbot ears. (see related question) The Processing room is to the left side. First go up, then left, then down. On your first visit to the room, you will probably be teleported out by the security system. Disable it and go back. (see related question) The Freezer room is at the bottom right, and contains the security system panel. Disable it before returning to the Processing room.
The map to the vent system is on the window outside, near the roof. If you don't have it, use the carrot transporter to go out and get it.
The power switches in the factory control the overhead crane. Push the center switch all the way down, and the other two halfway down, and the power will come on. Climb up to the large claw at upper left, and ride it right to reach the vent entrance. Inside, you can go left and right, and up and down. The fans at the bottom will raise you a ways into any shaft.
You need to go to the printing room (upper right side), and the processing room (lower left side). Eventually you will also travel to the Freezer Room (lower right side).
You have to get the cat for charlie, To do that go to the carrot farm, Go in the chiminie of the house, Pick up the bowl and go the carrot king area.. Then ask the girl for milk in the bowl, go back to the house, Put the bowl down.. go upstairs and turn the shower on, the cat will jump out. And you have to chase it to the milk, if its to hard to get it down stairs just keep clicking on the cat. then get the crowbar from charile when you return the cat.. And use it to pry open the vent. There.
Find the man's cat that is hiding in the farmhouse. Go down the chimney to get inside. Collect the saucer on the floor and get the lady in the restaurant to fill it with milk then go back into the farmhouse. Go upstairs and turn on the cold tap. A cat will come out. Try to scare it so that it falls down onto the ground floor. It will then drink the milk and follow you. Go back to the D.I.Y shop and give him his cat back. He will give you a crowbar. Go to the factory. Climb all the way to the top and jump down into the water. Then click on the manhole at the side of the factory. Once the lid is off go inside. You are now in the ventilation system.
Go to the abandoned farmhouse at the Funny Bunny Carrot Farm, to the left of Main Street on 24 Carrot island. Climb to the roof and you can enter through the chimney.
To get to the vent you have to go to the far right and open the vent with the crowbar that you got when you saved the store owner's cat. After that you go into it and win.