Spread a kitchen towel on the counter. Use your jar lifter to remove a jar from the canner. Pour out the water (save it for washing dishes), and place the jar on the towel. Keep the remaining jars in the canner, so they stay hot.
Use tongs or a slotted spoon to remove the potatoes from the pot and fill the jar while maintaining about a 1 1/2 inch headspace.
If using salt, add up to 1/2 teaspoon to each pint jar, and up to 1 teaspoon to each quart (salt is optional but adds a lot of flavor).
Add fresh hot water to the jar, leaving a 1-inch headspace.
Run your bubble popper through the jar to release any bubbles that may be caught in between the potatoes, and wipe the rim with a damp towel.
Center a lid on the jar, and screw on band until it is fingertip tight. Use the jar lifter to place the jar back on the rack in the canner, and repeat with the rest of the jars until the canner is filled, or you run out of potatoes.
Secure the lid, leave the vent open, adjust the heat to medium-high, and bring the canner to a boil. Allow the pressure canner to vent for 10 minutes, then place weight on the vent. Follow the directions for your pressure canner.
Once the canner has reached the correct pressure (10 pounds of pressure for weighted gauge pressure canner, and 11 pounds for dial gauge canners.), set a timer, and process pints for 35 minutes, and quarts for 40 minutes at altitudes of less than 1,000 ft. Adjust for your altitude if necessary (see note below). Regulate the heat as needed to maintain a steady pressure.
When processing time is complete, turn off the heat and let the pressure canner cool and depressurize. The time will depend on your brand and should be between 30 to 60 minutes.
When the pressure canner is depressurized, spread a kitchen towel on the counter, remove the weight from the vent pipe or open the petcock, and wait 10 minutes for the jars to adjust to the change in pressure.
While wearing pot holders, unlock the cover and remove the lid while tilting it away from you so that steam does not burn your face. Allow another 10 minutes for the jars to adjust to the change in pressure.
Use a jar lifter to remove the jars from canner and place on the towel. Keep the jars upright, and don't tighten bands or check the seals yet. The jars will be hot and bubbling. Let the jars sit undisturbed for 12 to 24-hours to cool.
Wait until the jars have cooled for at least 12-hours, and then check to be sure jar lids have sealed. Test the seal by pushing on the center of the lid. The lid should not pop up. If the lid flexes up and down, it did not seal. Refrigerate the jar and use up within a few days.
Remove the screw on bands and wash the jars. Label, date, store the jars in a cool, dark place (50 to 70 degrees F). Use within a year for the best quality. Yields 9 pints or 7 quarts.