Abstract: A system for testing a plumbing system for leaks includes a transparent cylinder at the top of a standpipe and in fluid communication with the interior of the standpipe so that when the standpipe and transparent cylinder are filled with water, and the water level subsequently drops, a leak in the plumbing system is indicated. The transparent cylinder is joined to the standpipe by a flexible, rubberized coupler that adheres to, or is clamped to, the standpipe and cylinder. The system avoids the need for a ladder provided the fill pipe is formed with a curved upper end so it can be hung on the wall of the transparent cylinder when the standpipe is filling with water.