Bill Maher ’s spilling the tea -- and, uh, more 😲 -- 'cause the comedian just confirmed those wild '90s rumors that he used to rub one out before filming his show ... saying it’s 100% true.

On his "Club Random" podcast with Cheryl Hines , Bill explained the only way he could sneak in a nap before filming his daily show "Politically Incorrect" was by, well, becoming "Politically Erect" ... so yeah, he was all about jerking off pre-show!

Bill dished the backstory -- saying his wild nights out clubbing left him dragging into work hungover and desperate for a pre-show snooze. Everything went smoothly ... until someone clocked his Jergens in the bathroom, and boom -- the story got out.

TBH, the admission tracks, 'cause Bill’s never been shy about sex ... even recently offering Gen

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