As I am sure other subscribers will testify, it is no real problem
to make a serviceable gauge out of transparent PVC tube (used for
fish tank aerators, and available from many pet shops).

The simplest form for vacuum is just a straight length, stapled to
a wooden lath to hold it taut, and with the end dipping into a large
shallow container, such as a bucket.  The slight difference in the
water level in the bucket as the tube fills can be ignored for most
of the sort of measurements needed, and a dye (such as fountain pen
ink or cake colouring) makes things easier to see.

Hope this helps,
Paul Morris
http://www.paulmorrismusic.co.uk/