Duct Mastic Installation Tip: Use a Workbench
It is easier to do a solid job sealing ductwork when you're standing at a bench instead of crawling through a crawlspace
After you’ve figured out the duct configuration for your ventilation system, it is time to seal the seams with mastic. But for sections of duct that are removable, by all means, remove them and set them on the bench for mastic sealing.
It is easier than squatting around a mechanical room, and you can do a superior job sealing the ductwork.
For ducts that must stay in place, take your time and glop it on thick.
—This video was shot on location at Professional Remodeler's 2017 Model Remodel.