After opening the dust cover on the cap,  place the key in its slot.  

Turn key to left and unlock.  

Once the lugs fit in their slots, turn the cap right and tighten as much as possible.

 Turn the key to right and lock , before  pulling back.

 Do not iassemble or dismantle by holding on the key.  

Clean the sides of  inner casing of the cap twice a month.

 In case the seal on cap is worn,  replace tank cap.