If it´s water based, a scourer and/or scrapper with plenty of water. For oil based paint, I would try a little solent & a rag. The only problem using solvent on plastic is that you remove a little of the plastic coating as well, leaving the area dull. Use a little solvent at a time & plenty of clean (not coloured) rags in a WELL VENTILATED area. If you use coloured rags you might transfer the colour onto the bin. Try a small area first. Solvent is extreemly inflamable.
Billy
January 2011