I'm using a brake vacuum check valve from like an '88 ford F150. It fits, and then I think it's 1/2" vinyl tubing down to the crank case and back up (U-shape) around the spine of the frame, ending between the pods. That tube is topped with a small K&N type gauze breather filter. Seems like there's always a scunge of oil film around that part of the bike, but it doesn't bother me much. I also did the old what's-his-name (Mitten?) mod to the breather itself and that may have been a mistake. Oh well, stuffed it with loose, coarse-grade steel wool.