I don't play bass but my friend does and we where listening to Sir Psycho Sexy and wondering what effect (if any) is Flea using during the first half of the song or so to make it all funky sounding.
It's an envelope follower, specifically the EHX Q-Tron.
I thought he used a Mu-tron with a dying battery in the studio, also the EHX bass-balls is said to get that sound.
Be sure to wear your erection with pride whilst playing.
i know back in the mothers milk/bssm era flea used a digitech filter as one of his main envelope filters too