videoman3857
Full time elf
If you want to paint plastic you have to properly prime. If in the US look for Bulldog adhesion promoter at you local Wally World. In Oz, look for Plastikote.
I primed one lot of conduit - cant remember what it was called, but it was a spray can.
I even went to the trouble of sanding the conduit to "key" the surface, but it still came off after a while.
I am currently experimenting with different water based paints.
I'll see if I can find that Platikote. - thanks for the heads up