A watertight, threaded through-wall fitting for anywhere a pipe needs to pass through a pond wall, skimmer, filter tank, or vault. This is the standard way to plumb a skimmer or return line through poured concrete or a rigid tank wall without risking leaks at the penetration point — eight sizes cover everything from a small 1/2" line up to a 4" high-flow line. Heavy-duty, corrosion-resistant construction with a compression gasket on both sides of the wall, so the seal holds regardless of which direction pressure is coming from. Specifications by size Model Pipe size Required hole size BF50N 1/2" 1.25" BF75N 3/4" 1.50" BF100N 1" 1.75" BF125N 1.25" 2.25" BF150N 1.50" 3" BF200N 2" 3" BF300N 3" 4.625" BF400N 4" 5.75" Every plumbing penetration through a concrete pond wall or rigid tank needs one of these — skimmer line, return line, or filter connections. Most builds need two or more.