New plastic fuel cap leaking

[Latech15]

I’m at the point of testing my tanks for leaks. Backs not on yet. When I fill it up with water, it is leaking in a pretty steady stream out of the fuel caps. These are the new plastic ones. Is there an adjustment that I’m missing here??

 

[Ron B.]

Tighten the nut that is under the cap. just takes a little.