Hydrogen sulfide is detectable by the human nose at VERY low levels, in the
parts per BILLION range, and as you seem to understand, it is the result of anaerobic decomposition of organic matter.
H2S itself, is a gas, and very volatile. It does not "hang around." If you have cleaned and aired out the part, and it still smells, it is because there are still bacteria in there making more of it in their private little hideouts. It is possible that the "stinky stuff" is also hiding in the piping...
If you clean it, really well, and rinse or soak with very dilute chlorine bleach, or an oxygen bleach product like Oxyclean, it will be gone. I prefer the oxygen bleaches, they are MUCH less corrosive to metal
parts than chlorine bleach. No extra "order neutralizing" products will be needed. H2S, and the bugs that make it, are very susceptible to oxidizing conditions, which is what bleaches do.
If the
boat is in the
water, use a wet vac to get as much
water out of the piping as possible between the closed sea cock and the strainer. Fill the strainer to the top with a bleach solution, and let sit for 4 to 6 hours. Open the sea cock and flush through the entire system well.
I am curious, why this matters? I mean, it has a tight seal on the top, who cares if their engine strainer stinks a bit? It shouldn't be getting out.