What do you suppose the maximum vacuum (in-hg) should be using something like this? I mean, it seems there may be a point of putting too much in there and 25 in-Hg seems like a lot of vacuum, where as something like 10 may do the trick...Just hate to do something and boom spring a leak somewhere (freeze plugs, thermostat, radiator, etc.) that was not designed for so much vacuum. Sounds like it works with that amount, but be interesting to know.
Otherwise, looks like a good idea and something a DYI could easily put together...I'd like it for getting all the stuff out of the block and such (never had any issues with air, as running the engine with the cap off (funnel if you don't want it splashing around) for a bit generally expels any residual). However, this is with oem type systems...When your filler is lower than the thermostat opening, then you should probably be using a remote filler or expansion tank. Otherwise, good luck getting the air out.