Abstract: The shower pipe assembly of the present invention can be used in a washing device such as a rotary drum filter and comprises an elongate pipe member including means defining a hollow interior flow chamber, preferably located adjacent a washer device, for conveying a wash liquid, preferably a liquid for washing a pulp mat. The shower pipe includes at least one row of spray holes extending through the pipe from the interior flow chamber to the exterior thereof. It also comprises a spray diffusion flange assembly extending from the pipe member adjacent each of the spray holes and further includes apparatus for impermanently attaching the diffusion flange to, and detaching the diffusion flange from, the pipe member, preferably to the exterior of the pipe member. These attachment and detachment steps are carried out without the use of auxiliary internal connecting apparatus which are not part of the diffusion flange structure.