Hood mounted air reservoirs for USA Trains 1:29 scale NW2 locomotive.
The tanks are 16mm polystyrene test tubes. I measured 100mm from the open end and cut off the bottom. There is a bit of a taper hence the 2 different sized caps and brackets. The piping is 14 gauge wire and Evergreen polystyrene 1/8" tube
The end caps are customized version of https://www.thingiverse.com/thing:953781
3d-Fuel Pro PLA PLA
My preferred method of preparing for paint is a layer of Squadron Green Putty, let dry and scrape with a hobby knife. Then 2 or 3 coats of Rust-Oleum Automotive 260510 2 In 1 Filler Sandable Primer (scraping/sanding in between).