Article by asasial of the XLFORUM ¹⁾
This should be done with the primary cover removed to keep the shavings from the drilling and tapping out of your engine.

• Parts:
  • 1/8“ MIP to 1/4” 90° brass fitting
    (any hardware store should carry these and you can also get creative with 90° fittings in your choice of brass or stainless steel)
  • 1/4“ clear tubing (or the milky colored tubing used for an ice maker works as well)
  • 1/8” pipe tap
  • Pipe dope

• Mark the holes for the length you want (the site tube should extend higher than the optimum oil level).
• Pre-drill the holes
• Tap the threads with a 1/8“ pipe tap (tapered thread)
  • Only run the tap in about half way and check your fitment.
  • If the fitting needs to go farther in, take it out and run the tap back in a little more and then re-check fitment.
    With the tapered pipe tap, the hole gets bigger the further you screw it in. Run it in too far and it can make for a bad fit and cause leakage.
• Install the fittings with some pipe dope on the threads and put a piece of clear tubing between them and that's all there is to it.

• With the bike on the kickstand, the level may be a little over the top of the tube. But, if you put a mark with a sharpie on your cover (level with the check plug towards the front of the cover) you will see where it should be with the bike level.
• Once you get use to seeing where it should be, you won't have to worry much about having a mark.

Primary Site Plug 2)