Slim Kärcher to osVAC Adapter. It uses my osVAC leak tight design, so you can insert a 37x32x2.5mm O-ring. If you don't have an O-ring at hand just leave it out, it will work as a regular osVAC coupling then. And the Kärcher vacuums have sufficient power so the tiny bit of leakage won't hurt.

https://www.thingiverse.com/thing:5347107

Remix of https://www.thingiverse.com/thing:4186480