1st of Tha Month E 1999 Eternal Bone Thugs N Harmony

take a fifth to the dome

A "fifth" refers 1/5 of a gallon of liquor. Fifths along with pints and half gallons are sold at most liquor stores. Taking something to the dome (or head) refers to using it all yourself. He drinks a fifth himself.
Referring to a fifth of liquir (probably vodka) straight to the head, with no chaser, which I wouldn't personally recommend. But hey, it's his head, not mine.
Fifth is referring to a liqour bottle size, the 750mL bottle. To the dome refers to the inebriatory effects on the mind.