Fuel System ?

[ModMX3 - (Carmaster2005)]

Ok so this may sound lazy, but i have just now got around to fixing my gas leaking problem after 2 years of leaking gas. 'i know'. It only leaked gas when tank was 1/2 full and around turns "i assume' . So i decided to pull the driver side wheel off and the plastic fuel fill cover, and descovered this neat rusted tube that had 3 fuel lines going to the bottom of it, its about a foot long and pinch welded at the top. I descovered a pin sized hole in it which i could smell gas from. so insted of paying an astranomical amount of money from a dealer. I decided to plug it and jb weld it. seemed to have worked. But my question is what is this tube and what does it do ? I have never had that pressure relief sound when i take off my gas cap, so im thinking this is some kind of expansion tank or somthing ? Any imput would be great. Would no tank pressure cause other fuel delivery issues ? Thanks !