[chrisguyw]

Hi Anthony, Painting polypropylene has always been a bit of a gamble, but see if you can find some Krylon "Fusion" rattle cans...........these are formulated for painting hard to paint plastics (plastic lawn chairs/pots  etc.), and, do stick quite well.

It has been mentioned above to sand with some coarse(ish) paper, but ,I would try to avoid this as polypropylene does not "Cut" well,.......it is more likely to "Shred", leaving little strings all over the place.............just give the surface a good clean with Isopropyl.

Cheers
Chris Walker