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).
Through the chimney
On the abandoned farmhouse, to the right of Main Street.
On the farmhouse to the left of Main Street, the chimney is the only way into the house.
The chimney in 24 carrot
Go left from Main Street and enter the farmhouse through the chimney.
You could get a house on Poptropica. But not a pet. To get a house you could get a house on 24 Carrot Island! It's on the carrot farm. If you complete 24 Carrot Island... you have a mystery roomate! You go thru the chimney to get in. Is that easy enough.
The farmhouse is past the Funny Bunny Carrot Farm, tothe left of Main Street. The house is closed up, but you can climb to the roof and enter through the chimney.
You enter through the chimney. The glass bowl is on the floor. You cannot walk past it.
sIMPLE YOU CLIMB THROUGH THE CHIMNEY.
The mayor of the town on 24 Carrot Island will give you the Island Medallion when you complete the quest.
24 Carrot Island is the 4th island of Poptropica. It came out in June, 2008.
The chimney is on top of the farmhouse to the left of the starting area.