No pump that is available can pull that kind of vacuum. 29.5"Hg is the lowest you will ever get with even the best electric pump.
I'm not sure what you call a giant compressor but 5-7 SCFM is usually sufficient. That's usually about a 20 gallon 3 hp compressor which is in the range of any serious car guy. I use a 5hp 60 gallon which is larger than most home units but I have friends that have larger garage compressors.
400 microns (usually a measurement of length) in pressure comes out to .4 Torr or .0157"Hg @0*C
Jefr
