Plastic tubing is extremely versatile because of its strength and ability to be easily cut with conventional tools. Standard extruded plastic tubing comes in a range of diameters, from 1/4-inch to 6 inches. Often, a cap or plug is needed to seal the tube's end. Plastic fabricators can build a plug or end cap, but it would cost be far more than the tubing. You can use a few basic fabrication techniques to create a seal or crimp for plastic tubing.
Measure the outside diameter of the tube to be sealed. Write the measurement down. The measurement must equal the diameter of the tube. Take this measurement to a plastics retailer and have it cut out a square of the appropriate plastic, 2 inches larger that the diameter of the tube.
Trace the outside diameter of the tube onto the sheet plastic. Leave the protective paper backing on both sides of the plastic while working with it. If the tube is less than 1 inch in diameter, measure the inside diameter of the tube, cut a 1/2-inch long plug from a piece of plastic rod, and proceed to Step 5.
Cut the disk out with a jigsaw. Use a fine-tooth jigsaw blade that has 10 teeth per inch. Follow the traced line, staying 1/32-inch outside the measured diameter. This allows the edge of the disk to be sanded without reducing the overall size.
Sand the edges of the disk by hand with 220-grit sandpaper to clean up any potentially dangerous sharp edges. Sand the edge of the tube that will be adhered to the disk with 220-grit sandpaper. Use a piece of scrap plastic or wood as a sanding block, moving the sandpaper in a circular position over the top of the tube. This takes some of the roughness away from the tube's lip, creating a better bonding surface.
Place the disk on a flat work table. Apply a thin bead of acrylic gap-filling cement to the face of the disk, running the bead along the outer circumference of the disk's face. Place the tube onto the glued side of the disk, checking to make sure the tube and the disk's edges line up. If the tube is built into a wall or other vertical surface, use painter's masking tape to hold the disk in place after cementing. If plugging a small tube, apply gap-filling cement to a plastic plug and insert the plug into the tube. Allow four hours drying time for either method.
Apply a small bead of cement to the outside gap between the disk and the tube, to reinforce the joint. Allow 24 hours for the cement to completely cure, and the project is complete.
If the tube is made from soft, flexible plastic, the end can be crimped rather than sealed with a plastic disk or plug. Heat the tubing over an open flame until it becomes soft. Remove the tubing from the flame. Use a pair of small pliers to crimp the tubing together. Hold it under cold water for two minutes until the plastic cools down. Two-part epoxy glue can be used to fill any small gaps in the crimp to make it watertight.