I've got a classic 2213, and it came with metric tubing; 18mm outside diameter (OD), and 12mm inside diameter (ID). This makes the tubing slightly smaller than the standard 5/8" OD - 1/2" ID. You don't want to buy additional tubing and attach it directly to the filter or any attachments, since the replacement tubing is larger than the original. But you can use the 1/2" male to male barbed connectors. Cut the line you want to extend, place a barbed connector in each side and use your replacement tubing in the middle. To get the smaller metric tubing onto the barbed connector, drop the end of the tubing into boiling water for a few seconds.