Vans VA-107 brake fluid reservoir. It's a cylinder with two bungs welded to it. Typical orientation is opposite of what you show in the picture. Nothing magical about the device -- it just holds a few ounces of your favorite MIL-H-5606 or whatever...
Here's a typical installation:
Normally the vent is at the top, inline with the major axis of the cylinder, and the output is at the 90° location at the "bottom". Nothing prevents you from flipping it around and changing the comes-into-from-the-goes-outta....
Remove the top plug & insert a dip stick. I have used everything from a narrow screw driver, piece of wire, sliver off a popsicle stick, what ever is handy. I fill the reservoir to about 75% full- don't fill it to the top!
You might consider eliminating the firewall mounted brake reservoir and the plastic brake lines from the firewall to the master cylinders. You can install individual brake fluid reservoirs on the master cylinders. Since you have an RV-8 you can remove the front baggage floor for easy access and check the fluid levels with a white zip tie which will show the red brake fluid nicely. Like many have done you could also make a large access panel on the front baggage floor. I just did both of these during the caliper O ring replacement (Vans service letter SL-00047).
I also copied someone’s idea here on the forum and used a fitting screwed into the top of the reservoir with a clear tube running to the top of an old peanut butter jar. Pump from below at the bleeder valve until you get no more air bubbles and you’re done. Be sure to seal everything well with appropriate thread sealer.
So much cleaner and easy to service.
