Check valve:
Dorman 47149 at NAPA, Autozone, O'Reilly's, Advance, Summit, etc.
https://www.amazon.com/Dorman-...-Valve/dp/B000COCU0M
I've been using one for almost 20 years (I got it in a salvage yard from a Ford V8). They're used all over the place in a lot of cars.