Amongst many other things I build fuel tanks for model aeroplanes. These are tinplate fabrications soft soldered together using 50/50 plumbers solder and Bakers Fluid. The tanks must be pressure tested to ensure there are no leaks, then they are flushed out two or three times with a strong solution of hot water and bi carb soda. Then they are pressure rinsed with clean hot water, then dried as far as possible, obviously drying internally is a bit difficult. At this point the tanks are very clean and susceptible to rust, so the get a light spray with oil, inside and out.
Job done………..finally
cheers
Bill