A drainage pipe to be inserted into the ground, presents a plurality of openings (5) for the passage of water, wherein each of the openings is closed by a cap (9) containing one or more holes (11) filled with water-soluble material (13), adapted to prevent the passage of debris during drilling, which the material dissolves in contact with the water in the soil. In particular, the caps have a hollow body (9) with a plurality of holes (11) in the wall for the passage of water, which the body and holes are filled with water-soluble material (13). Moreover, the caps present an undercut (12) on the end wall of the cavity, to prevent the exit of the water-soluble material (13) which fills the hollow body (9).