HO Scale Dust Filter for your Industrial Layout. Go to:
https://www.shapeways.com/product/59UU5S2C4/ho-scale-dust-filter-ductwork-variety-pack to order the variety pack of 90 degree elbows, 45 degree elabows and the transition piece.
Hint: Soak overnight in Bestine prior to painting. Not intended for children under age 14.