Most of us install fuel dots on a 3rd line. This is easily done on fuel tanks with brass tubes. Bend the fuel dot brass tubing to the bottom of the tank so you can suck fuel out after flying.

If you use one of the tanks with fixed plastic nipples, you won't be able to de-fuel unless you invert the plane or stand it on its nose. With a low wing plane, you can de-fuel with the plane inverted in the cradle after you take the wing off.

To use a dot in the normal feed line with the T in the line, you'll need to clamp off the line to the carb with hemostats so you don't flood your engine during fueling.