Abstract: A caulk gun having a piston with a flexible rim providing dripless dispensing of caulk or adhesive and including a tube-engaging receptacle for securely holding a tube is disclosed. The advantages of a dripless caulk gun are provided by a piston having a flexible circumferential rim that engages an inside surface of a caulk or adhesive dispensing tube to create an atmospheric seal. The plunger moves the piston against an inside movable surface of the dispensing tube. When the trigger is released, the plunger mechanism moves backward, and the piston creates a partial vacuum within the caulk tube thereby halting dispensing. The dispensing tube is attached to the caulk gun by secure engagement with a tube-engaging receptacle. The receptacle may be provided with threads that threadingly engage with a portion of the dispensing tube.