Can I run Petrol or Diesel through TruDesign fittings ?

YES and No
TruDesign fittings (in both black and white) are suitable for contact with petrol & diesel fuels.
NOTE: TruDesign Ball Valves, Aquavalves and Non-Return Valves should not be used in direct contact with petrol or diesel as the nitrile o-rings may swell affecting their sealing and handle-turning performance.