Unvented gas tanks

[briansnat]

I bought a new gas plastic gas tank for my outboard and the thing is not vented. That causes the tank expand like a balloon on a hot day. The thing looks as if it is about to explode.

Are unvented gas tanks a new regulation or did I just get a cheapie? If this is the wave of the future it's a stupid one. I can see one of these things bursting if it's a hot enough day. I tried to remove the cap to vent it a bit and it blew 5 feet into the air.