A strip of membrane material is laminated to a wider strip of netting and then the longitudinal edges of the strip of netting are seamed together into a sleeve for receiving aggregate to form an elongated tubular drainage element. The laminated peripheral portion of the resultant sleeve is used as the top of the drainage element to preclude fine material from entering the drainage element. Where a membrane is used to form the sleeve, holes or slits are placed in the peripheral portion of the sleeve that is to form the bottom of the drainage element. The seaming of the overlapped longitudinal edges of the membrane is effected using glue and a nozzle that blows air under pressure onto the seam to force the edges and glue to bond together.