Yes, canning can be exhausting, but that’s not what is meant by exhausting (or venting) a pressure canner.
Dry air trapped in a pressure canner lowers the internal temperature and might result in underprocessing. To be safe, USDA recommends all pressure canners must be exhausted 10 minutes before they are pressurized.
Load the canner with filled jars and lock the canner lid in place. Leave the weight off the vent pipe or open the petcock on older models. Heat the canner on high until steam flows from the vent. When a visible funnel of steam flows continuously, set a timer for 10 minutes. After 10 minutes of continuous steam, close the petcock or place the weight on the vent pipe to begin pressurizing the canner. Learn more at www.bookstore.ksre.ksu.edu/pubs/MF3242.pdf.