Take your drill and drill a line of holes down the length of the pipe that will span three sections of 2.5" diameter. Don't press too hard or you may shatter or split the PVC. Run the bit through the top and continue to drill on through the opposite side of the pipe.
Once you have drilled one set of holes turn the pipe 90 degrees and drill another line of holes. The holes can be anywhere from 1/2" apart to 3/4" - this is not critical.
This long piece will then be cut into individual sections... then these will be placed in the bottom of the bucket... once soil has been filled in these sections will allow the watering pipe to fill this area with water for the plant.