After pulling the trigger, the plunger (metal rod that pushes the tube's bottom) locks and does not retract. There is remaining pressure on the sealant material and that's what keeps the sealant flowing. The result? Huge wastage!
Anyway, after inspecting the gun, I realized the release tab at the back of the gun that allows you to pull the plunger also allows you to release the pressure on the sealant material inside the tube. So the best thing to do after each rest or stop, push on that release tab with your thumb as shown below. Then pull back the plunger a little to ease up the push on the tube.
For more info on how to use a caulking gun click on here.