Cheap insurance to protect against dirt in the fuel injection system is to make sure you've got good filtration. I've always thought having one of those sock filters would be a good way to catch any debris or other shit that might come from the underground storage tanks at the gas station, or other ways crap can find its way into your tank. As I was filling my DR650 one day a few years ago, a clump of mud fell from the visor of my helmet into the fuel tank. Nice.
Anyway, for $30 plus a couple more bucks for shipping, I ordered one from from Profill-Australia: Specifically, I bought part # MK3 KTM0002 which states that it fits "under" the billet aluminum filler neck that they sell. I have a similar aftermarket filler neck (mine is made by CJ Designs) but it basically mounts the same so I figured it should work. This would not work if you are still using the junk OEM fuel cap. Throw that shit away.
Just under 2 weeks to arrive in the mail. Not bad considering it traveled 1/2 way around the world.
Installation was pretty simple: I removed my aftermarket fuel filler neck, dropped the sock down into the tank, and re-installed the filler neck. The plastic collar around the sock wiggles around a small amount but it can't fall inside the tank, so there's no danger of going anywhere. Total installation time: 5 minutes.
The next day, I learned that I had grossly underestimated the annoyance factor in the extra time required to fill the fuel tank. Holy fuck! Ten minutes to get 10 litres into the tank. If I try to squeeze the gas pump nozzle to flow any more than a small dribble, not even a trickle, the result is gasoline spilling everywhere. I expected it to be slow -- but it's beyond ridiculous. Filling up using an eye dropper would be faster. That being said, I do realize I'm whining about first world problems. I'll have to accept extra time at the gas station to keep the fuel system clean.
This arrived in a small bubble-wrap envelope.
Fabric looks and feels like sating or silk.
Here's my aftermarket filler neck, made by CJ Designs,
with Acerbis screw cap.
Here I removed the filler neck, and dropped the sock inside the tank.
The plastic collar on the sock prevents it from falling inside the tank.
Now the filler neck has been re-installed. The sock is sandwiched
between the top flange of the fuel tank and the billet filler neck.