2nd picture showing gas cap end. I purchased a 2nd gas cap and modified the orignal. This way I can use the generator
with or without the 2nd tank.
I removed the vent switch and gasket from the gas cap, threaded the fitting into the cap and JB Weld the fitting in place to seal it. Once dried I replaced the gasket and pressure fit plastic tubing into the brass fitting that is rated for gasoline.
Marine gas tanks are better quality and with the vent open fuel will not come out unlike a regular gas tank that some of the generator suppliers are selling.