My bathroom wash-basin sits on a plinth, the U cross-section plinth, has a gap between the rear of the U and the wall is around 3 or 4 inch, leaving the ugly pipes exposed and on show. Long ago, I cut a pair decorative faced ply-wood, just to slip in at each side of the pipes, H + C + waste straight out through the wall, just to hide the pipes. A box shape over the pipes doesn't work, due to the angles, the thickness of the U and the pipes being partially protruding into the U. The flat ply panels do sort of work, but have to thread in at an odd angle. How are such pipes normally hidden?