I'm pushin' my fort
This refers to how, Kendrick was (and still for the most part is, until Oxymoron drops) carrying the weight and popularity for the TDE camp as a whole.
For further evidence just look to twitter, he’s amassed more followers than ScHoolBoy Q, Ab-Soul, Jay Rock, Punch, and Top Dog all combined. Not to mention this version of the song was released to capitalize on the popularity, attention, and impact that BDKMV and GKMC had.
Alternative understanding: I’m pushing my fart, carrying on the previous lines of bathroom wordplay.
To help improve the meaning of these lyrics, visit "Bitch, Don't Kill My Vibe Remix" by Kendrick Lamar (Ft. Jay Z) Lyrics and leave a comment on the lyrics box