make a manual vacuum pump for under $20 by converting a bicycle pump

Step 2 Reverse the piston disk

To reverse the piston disk, unscrew the cylinder top, and pull the handle out all the way, so that the the piston disk comes clear of the cylinder---be careful, it's greasy. You don't want to lose the grease and get it all over other things, so prop the shaft up with something to keep the piston disk off your work area. Have paper towels or something handy.

Notice that the piston disk is actually a shallow cup shape, with a lip around it. That lip flares out and seals against the cylinder on the downstroke.

Now

(1) Unscrew the nut on the end.

(2) Pinch the rubber and metal disks together, and pull them off the end of the shaft.

(3) Turn them around.

(4) Put them back on the shaft.

(5) Replace the nut and tighten it up, hand tight.

Now you need to get that stuff back in the cylinder, and you don't want to scratch the piston disk on the sharp inside edge of the cylinder, so:

(6) Pinch the rubber disk from the sides, into an oval shape,

(7) Angle the shaft and the disk about 30 degrees relative to the open end of the cylinder, and insert one end of the oval, and

(8) Gently work the rest of the disk into the cylinder, pushing it inward anyplace it seems to catch on the edge, and straighten the shaft.

Now you can wipe the nasty grease off your fingers.

(9) Push the handle in some, straight, and

(10) Screw the cylinder top back on.

You're half done.