Painting Clear Plastic Bottles/Flasks/Test Tubes

[GIDave60]

Hello my friends, it has been a while! I am going to begin working on a few kits that have clear plastic beakers & flasks, etc. I found the post regarding gluing & polishing them, but I recall something posted regarding painting/filling them so they look like they're filled with liquid, or a way to make them look like those old brown glass bottles? Any guidance will be appreciated, nice to be building kits again