We will need to select a dye that is suitable for the purpose. Drain dyes are typically available in various colors, but for detecting leaks, a bright and easily visible color like fluorescent green, red, or blue is what we find works best. Drain Dye is a water colourant used to locate leaks in plumbing, tracing pipe locations, detect drain damage and water pathways. It is non-toxic to the environment and odourless.