Simple, cheap and very useful, fits every chemex size and no more vacuum to deal with. You could use a straw, but for 3$, save yourself the trouble and use this

It's just a plastic clip, but it's a cheap way to improve your Chemex experience. It also keeps the filter in place when rinsing.
I've been using the Chemex for years and never knew this existed.

Not much to it, it's a plastic clip; fairly robust, fits flush onto the chemex, and does what it says. I have the 8-cup with the handle and the clip sits nicely over the handle without getting in the way.