VPI 16.5 vacuum cleaner

Call VPI they will tell you how to proceed.

I have to ask, have you removed the clamp from the drain tube?

Thanks.

Yes.

I have sent a mail to VPI for advice.

Thanks.

Mine is about 10 years old and I've never had any problems with draining the fluid.  After draining I regularly flush mine out further with water.  It sounds like the drain going out to the hose might be clogged.  Might want to check again with VPI to see what their recommendation is if the drain is clogged. 

Sounds like something clogging the outflow of the tank.  Might gently flush a little water back up the tube to see if you can dislodge the obstruction.

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.