[Werner]

Ian,
thanks for the advice. I was thinking about this T-valve. But the problem is that I am not getting suitable US thread inches for the fittings.
But it's not a problem now that I know how big the pollution is. The large amount of dirt shows that my idea with MMO and scraping brass nuts is gradually removing the dirt. I just have to clean the drain housing more frequently.

Dave,
our fuel purity at the fuel dispenser is beyond question.