Measure twice. Install it once.
Use it LOTS.
When choosing what size to buy for your Gleco Trap, the only limitation is the space available under your sink. The plumbing under your sink may not exactly match the diagram below, but youll almost always find a pipe down from your sink going into a U-shaped joint called the P Trap. After the P Trap, an elbow joint turns the pipe so it runs horizontally into the wall. Measure the space between the floor and the center of the horizontal pipe right after the P trap. That measurement tells you how much space is available for the Gleco Trap.