Thanks, Grooveman.
I don’t have the new booster at hand yet. However, I think the diameter of the elbow/valve is 13 mm. Anyway, the diameter of a separate check valve is 13 mm. So, maybe it is good to use a hose with 13 mm inner diameter and a suitable hose fitting which will be screwed into manifold. I am just a bit confused since some people have apparently used 1/4" and 11/32" hoses. 