I may not have used the best for degreasing. But I have a bottle of Eagle One car shampoo mixed with water that I use when clay barring. I used that and a brush on my bumper insert.
(I know, car shampoo isn't the best for degreasing since it's supposed to leave vital oils for the paint intact. I didn't stop to think about it at the time, but it seemed to take okay, lol.)
wash it good in soap and water then sand it down as nessacary. go to walmart and buy a tack rag from the paint dept (if you dont know what it is ask the paint guy) it will remove any olis and all the sawdust that was left by the sand paper then primer and paint as you see fit hope this helps