Pressure build up in fuel tank - Normal??

2001 JCB series 3 backhoe that has a fuel leak. I know where the leak is and what is causing the leak but I'm not sure what the real problem is.

Here goes: when sun hits the fuel tank in the morning, tank warms up and pressurizes the tank. (think of a plastic fuel can that swells up when left in the sun) This pressure build up causes fuel to leak out from the top of the fuel sediment bowl. (not sure if a fitting or seal or ??) If I loosen the fuel cap overnight, no leak the next day....

Pressure build up in fuel tank - Normal??

Pressure build up in fuel tank - Normal??