im pretty sure it would be ok for water traps but, i believe someone (Daniel E. i think) said that they sometimes use fish oil in the paint mix and that you can smell it..i dont know if its true but i dont use it so i wouldnt know...
Rustoleum's Rusty Metal Primer contains fish oil.
Here it is from Rustoleum Company:
"Rusty Metal Primer
The original and the best, based on Rust-Oleum founder Captain Robert Fergusson's discovery of raw fish oil's ability to stop rust and prevent corrosion on metal ship decks. Unique fish-oil-based formula penetrates rust to bare metal, to drive out corrosive air and moisture other primers leave behind. Bonds tightly to rust to form a surface that topcoats can adhere to."