My coach is a much different entity, Sigbert, but I’m guessing your two lines are for draining moisture from two tanks, the “brake” tank and the “accessories” tank. The other line, that you refer to as for the brake release, may have a quick connect fitting. Tow companies might use that to pressurize the tanks, allowing them to keep the brakes off. Hooking an outside compressor to that fitting should fill both tanks, so you can air level or raise the coach. You can also use that fitting to connect an airline for topping off tire pressures, but there's a trick to that and that's another story.
Others here more familiar with your configuration should speak up soon. My rig has the quick connect tank fill, and 4 drain spigots (lines) for the two tanks that each have “wet” and “dry” sides to them. As noted, yours is different. But you should still be able to remotely fill the tanks and have means to drain any harmful moisture from them every so often. I understand some coaches have moisture drain valves on the tank undersides; owners must either crawl underneath to open them or use remote wires with T handles. A properly operating engine compressor/air dryer should keep moisture out of the tanks, regardless.
Joel
