Abstract: An apparatus for discharging a high pressure burst of air against a column of standing water behind an obstruction in a drain line to create shockwaves in the water column to remove the obstruction, including a hollow gun body having a discharge opening and a pistol grip handle connected to the gun body. A discharge valve is connected to a piston dividing the interior of the gun body into two chambers, the pressurization and de-pressurization of which is controlled by a trigger operated pilot valve. Air is quickly exhausted from a rearward chamber by depressing the trigger and pilot valve, causing the piston and valve to snap rearwardly to open the discharge opening and direct a burst of pressurized air from a forward chamber to exit through the discharge opening and into a drain line.