VPI 16.5 vacuum cleaner

If it is like my old 17F, you can unscrew the unit from the bottom. It will reveal the entire line and you can check to see what's wrong.

If it's old and has had a lot of use, you might consider replacing the tubing with a new piece, available at Lowe's or HD for a couple of bucks. Once you unplug, turn on its side, it's pretty easy to do. Cheers,
Spencer

As mentioned, I would first suspect the drain being plugged. If you have the means to blow compressed air up the drain tube, even blowing by mouth(clean the tube first of course). It really shouldn’t take much pressure to dislodge any debris. Once you get it flowing again, flush the tank and enjoy another 10 or so years of record cleaning.

Problem solved.

Thanks to all.