An apparatus and method for sealing joints and leaks in pipes is provided. The apparatus is particularly useful for sealing leaking at joints in underground gas mains. A sealant applicator in the form of a push snake is provided which may be inserted into the pipe through a standard tap fitting. Thick or viscous sealant is pumped down through the snake and is thereafter applied radially outward to the inside surfaces of the pipe by a spinning applicator tip. Flaps may be attached to the spinning applicator tip so that the thick sealant is trowelled into place. The applicator tip may be rotated with compressed gas which may be compressed methane gas drawn from the gas main. A centralizer is preferably employed to centralize the applicator head in place during application of the sealant. The flaps may also be used to clean the pipe prior to the application of the sealant.