A float valve assembly is provided which can be remotely retrofit to a pipe end located in a production tank. The valve assembly comprises a guide rod disposed axially in the valve assembly. A floating valve element of the valve assembly is coupled to the guide rod and is moveable with or axially along the guide rod. The valve assembly is remotely mounted on the pipe end by temporarily associating an installation tool with the guide rod to locate a fitting adapter of the valve assembly over the pipe end for sealably fitting the valve assembly to the pipe end. The guide rod can also be manually manipulated for moving the valve element away from the pipe end and locking the valve element in the open position for permitting flow of liquid through the pipe end. A method for manually locking the valve element in the open position is also provided.