It is universally recommended that the basement be completely opened to the outside in order to provide a free and unrestricted flow of air to the duct leaks. Another variation of this theme is useful in testing for duct leaks to the outside of the house. This can be done quickly by sealing the registers and removing the pressure barriers between the house and the basement by opening a door between these two zones. With the blower door running, the ducts are then all in the same pressure zone with respect to the outside. The only source of leakage flow is from the outside of the house in this case, and the leaks to the outside are revealed if a pressure difference of more than 5 Pa develops between the house and the sealed ducts.
Special equipment can shorten time spent measuring pressure drops across multiple zones .
This can be made from widely available materials. It's often necessary to run a tube between a zone and the place where a pressure gauge is being used to take readings to estimate leakage. Suppose one wants to see how leaky the basement is to the outside word and to the inside of the house. And in the same house, one also wants to see how leaky the ducts are to the outside of the house and to the basement. It is advantageous to run the series of tubes from each of those locations back to a central location, such as near the blower door.