Hercules® Megabubble® leak detector uses a high-viscosity formula that produces large, long-lasting blue bubbles for easier detection of leaks on pipes, fittings, tanks, coils, cylinders, pressure vessels and valves. The formula is non-toxic, non-corrosive and will not freeze. Plumbers have come to trust the Hercules offering to provide the highest quality thread sealants and other plumbing products.