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

Step 6 (Optional) Drill the hose fitting out a little

I decided to make the hole through the hose fitting a little bigger, to reduce any resistance to air flow.

This doesn't make much difference most of the time, because the resistance there is usually small relative to how hard you have to pump anyway, for any substantial vacuum level. It does make rapidly pumping larger volumes of air at lower vacuum levels slightly easier. (Like near the beginning of evacuating a vacuum bag or the vacuum tank for my vacuum former.)

At any rate, I just drilled through the existing hole with a 1/8" drill bit. As usual with drilling metal, you should to do that in little spurts, at fairly low RPM's, and frequently pull the drill out to get shavings out of the way and let the bit cool. This took about a minute of drilling in several goes spread out over a few minutes, drilling from either end while holding the fitting firmly with a wrench. (I used titanium-coated but very cheap drill bit from Harbor Freight.) If you drill too fast, or for too long, you'll just heat things up and dull the bit faster.

Once you've drilled it, blow the metal shavings out. You don't want them getting in the pump.