Best way to clear grit and sand out of 7 pin plug??

To answer your question I use a drill that fits inside the hole and just twist it by hand. It will also remove corrosion. That fine sand caused more problem for my tow bar and prevented it from locking. No amount of WD-40 would clean it. I had to disassemble it and was amazed at the amount that got by the seals. That sand/dust also got into some of my baggage compartments passed the seals. There were a lot of dirt roads up in Alaska.