Method of covering corrugated drainage tubes

Claim 1

In the subsurface drainage of water from land wherein corrugated drainage pipe having alternating peaks and valleys and a plurality of openings in selected valleys arranged along the longitudinal axis of the pipe is buried beneath the surface of the ground, the method of preventing the pipe and its openings in selected valleys from becoming clogged with gravel, rock, mud, dirt and the like which comprises providing a length of pipe of the type described having a desired maximum diameter, providing a length of tubular knit fabric corresponding in length with the length of said pipe and having a maximum diameter in the relaxed condition less than said desired maximum diameter of the pipe, installing said tubular knit fabric on said pipe, and permitting the tubular knit fabric to relax into snug, tight engagement with the peaks of the pipe with intervening undulations of the tubular knit fabric extending inwardly toward the axis of the pipe in correspondence with the location of said openings as the tubular knit fabric spans the valleys of the pipe.