Use smoke. A smoldering piece of cotton rope will do.

As far as a tune up goes. Get rid of the 4" tuding and replace with 4" or
6" spiral or PVC pipe. That tubing is killing your performance.

Phisherman wrote:

Any tips on how to detect DC leaks? I use a 1.5HP DC, a pre-DC
cyclone garbage can, corrugated 4" tubing, blast gates. I was
looking for a step-by-step DC tuneup.