Quote Originally Posted by Ben Rivel View Post
I dont think youd have to make a hole in the dust collector, just the incoming ductwork going into the main inlet.
I think the pressure at that point under most operating conditions won't be low enough to keep the bag pressed against the barrel. The pressure you're tapping into has to be lower than the pressure inside the bag. That pressure is essentially the same as the pressure at the bottom of the vortex.

As the air enters the cyclone it expands thus increasing static pressure. As it flows around and down there's pressure drop due to frictional losses. Unless your duct is really small compared to the inlet that loss will likely be more than the expansion gain.

On the way up the inside of the vortex and outlet tube you get both contraction and frictional losses. The top of the outlet tube should have a lower static pressure than the bottom of the vortex. I think a tap here will do a much better job of keeping the bag inflated.