Filling and bleeding break line on a dirt bike, how to?

a brake bleed pump kit is almost mandatory for this, or even just a length of clear plastic hose. or a speed bleeder bolt is the absolute BEST, makes the job super easy. anyway 1. take the reservoir cap off, top off the fluid. 2. attach your clear hose to the caliper bleeder bolt (lubricate it with vaseline so air won't infiltrate) and put the other end in an empty container to catch the fluid. 3. pump the brake lever three or four times, and hold on the last time. you should feel pressure in the system. 4. with an open ended wrench, loosen the caliper bleeder bolt slightly until you feel the pressure in the brake lever lower, and then quickly tighten it back up. repeat steps 3&4 until you get constant fluid with no bubbles coming out. if you had totally drained the system, it could take a long time doing it this way. What I would do in that case is inject brake fluid directly at the caliper. use one of those curved tip medical irrigation syringes, fill it with brake fluid, and then hold it firmly into the hole where the caliper bleeder bolt goes (if you have a rubber washer that can help seal it) keep doing this until you get fluid seeping into the open reservoir. This is the quickest way to get the fluid back into a dry system air-free. you will still need to bleed after doing this though, it just makes the process really quick. but if you get the speed bleeder bolt then you don't even need to do that, just loosen the bolt at the caliper, and pump&release away at the brake lever until you get fluid

That's BRAKE line. You don't cap the reservoir. If you do, you won't be able to replenish the fluid supply as it drains into the line. And, as you've discovered, it won't drain into the line. Don't cap the reservoir until the fluid runs clear (i.e. no bubbles) at the other end. Don't forget to keep filling it. You can also buy brake bleed kits at auto supply and bike stores. They make the job easier.