In the state of Montana (perhaps elsewhere, I'm not sure) dirty 30 refers to a 30 pack of Keystone Light. Cheap shitty beer that all the hicks LOOVVEEE.

Rasheed Wallace, number 30, forward for the Portland Trail Blazers NBA basketball team. In the world of sportswriting, Sheed is frequently criticized for his large salary, marijuana citation, large collection of technical fouls, suspensions, altercations and a racially charged Oregonian interview where he said the NBA exploits African-Americans.