Cut the pipe. Decide how short to make the markers. Measure the pipe, and make a mark where the cut needs to be. Use a heavy duty knife to cut through the pipe. Cut the pipe cleanly and evenly.
Create the threading. Use the threading tool to thread both ends of the pipe. This allows for the caps to screw on. Threading both ends is necessary, since a cap goes on one side for refill, and one side to cover the tip of the paint marker.
Determine the thickness of the paint. The ratio of carpet to sponge depends on the thickness of the paint used. If the paint is thin, use more carpet. If the paint is thick, use more sponge.
Cut the carpet and sponge so that they are an inch or two shorter than the length of the pipe. Lay the carpet out flat, and put the sponge at the top. Roll from the top down, keeping the roll tight. The end result should fit tightly in the pipe. It may take a few tries to get this right, but if it is too loose, it will fall out of the pipe, and make a huge mess. The carpet and sponge tip should stick out ¼ to ½ an inch.
Break in the tip. Rub the tip of the carpet and sponge on sandpaper or rough concrete. This helps the paint spread easily across the top of the paint pen and onto the paper.
Fill the paint marker. Cover the tip end of the marker, and open the bottom part. Fill the pen with the paint of choice, and replace the cap on the end.