does anyone know where theres a diagram (or info at all) on how the vacumatic filling system works? also, does it vary largely from the Vacumatic to the 51?

I think there is a diagram on Richard Binders site. The vac mechanism in a vac and 51 are pretty much the same. That said there are numerous vac mechanisms in a vac, plastic button, lock down, etc.

The vacumatic filler in a 51 and the Vacumatic models are interchangeable. Both work with a breather tube as well.

Check Richard Binders site, the best explanation of this model I have seen is there.

Cheers,
Sean