There is a circular 1-inch hole abour 6 inches above the brake pedal. It usually has a foam/carpet plug over the top of it.... and then a rubber grommet sealing it. Don't remove the grommet... drill through it, and then run your tubing.
Splice the T-fitting into the small line (3/8, maybe 1/2 external diameter) coming off the side of the factory BPV.
And then sell the Glowshift gauge.
There are plenty of budget-minded gauges out there that won't cost you much but will be MUCH better quality.