Cam'ron wants to be No. 1 when you go No. 2 ... courtesy of his latest venture -- the toilet paper biz!

The rapper tells TMZ he's already dropped $21K for a machine to manufacture the paper, and plans to buy 2 more. When he first announced the idea with DJ Superstar Jay & Gray Rizzy on their SiriusXM show, some people thought it was a joke ... but he's serious.

How serious? Cam says, "When it's time to take a s***, you don't want no paper cuts in your ass. It's a real problem." He's promising AT LEAST 2 ply comfort.

Cam'ron's brand, Dipset U.S.A., already hawks shower curtains, towels, various toiletries and even Ebola masks. That new nickname ... "Bed Bath and Killa" ... really fits.