That is a vacuum brake bleeder. It pulls the fluid through vs. pushing it through. I've read that air can get sucked in past the threads of the bleeder screw with the vacuum style. Don't loosen the screw any more than needed to get fluid out.

The vacuum tester is a very useful tool to have.

Pressure bleeders can be made easily with a pump type sprayer and a Benz brake fluid cap.

Good luck!!!

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