Sometimes a little piece of debris can get caught in the system which prevents the dripper from sealing up completely, causing a drip. The fix is an easy one. Start by placing a colander or bowl  under the dripper. This is just in case something drops as there are three parts inside: two rods and a stainless ball.  Hold the dripper at the tip and unscrew the outer half of the dripper counterclockwise.  The dripper will split in half, leaving one half fixed to the pipe. Wash all of the parts, including the piece of the dripper that was removed, with some white vinegar. Make sure that nothing is caught down in the dripper. To reassemble, place the long rod in the dripper half still connected to the pipe, making sure it goes back through the dripper half and points into the pipe. The short rod points out to the birds and the ball is inside the dripper. Don't over tighten the dripper, just snug it up.