This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Where liquid is run through a funnel into an opaque bottle or earthen jug, the filling cannot be watched, and if not watched constantly, the vessel will overflow. This can be obviated by applying the automatic valve to the funnel stem, as shown. A washer support is soldered or otherwise fastened in the upper end of the stem, or at the base of the sloping part, and a crossbar is fastened to its upper surface across the hole. The crossbar is centrally drilled to receive a small rod or wire, to which is attached a valve that will cover the hole in the washer. A cork is stuck on the lower end of the rod. The location of the cork on the rod should be at a point a little below the level to which the bottle or vessel is to be filled. - Contributed by H. W. Hilton, Hopington, B. C.