The shut off valve assembly is attached direct to carburetor.
Are you by chance referring to the fitting with filter that screws into
tank? If so, that would be a toughie as the filter component is often damaged
or missing. In line filter as used on outdoor power equipment can be
installed in fuel line. Those with soldering skills can fabricate a brass
screen filter to go on fitting.
If the fitting filter is clogged soak in lacquer thinner.
Operating without a fuel filter is not recommended.
If fuel line enters compression fitting at an angle other than 90 degrees
the fitting will leak, tightening the fitting to stop a leak may damage
the fitting and not cure the leak.
Louis