Lay a 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.
Place the canning funnel on the jar and raw pack the sweet potatoes into the jar while leaving 1-inch headspace.
If you are using canning salt, add up to 1/2 teaspoon salt per pint jar and up to 1 teaspoon per quart jar.
Ladle boiling liquid over the sweet potatoes, and fill the jar while maintaining a 1-inch headspace.
Remove air bubbles with the bubble popper, and wipe the rim with a damp paper towel. Make sure all the pieces are submerged and adjust the headspace again if needed.
Center a cover on the jar, place the band over the lid, and screw it on until fingertip tight. Then, using your jar lifter, immediately place the jar back in the canner, and repeat with the rest of the jars until they are all filled, or you run out of sweet potatoes.
Place the lid on the canner and lock it. Leave the vent open, adjust the heat to medium-high, and bring the canner to a boil. Allow the pressure canner to vent steam for 10 minutes, place the pressure regulator on top of the air vent, and let the pressure rise.
Once the canner has reached the correct pressure (10 pounds for weighted gauge and 11 pounds for dial gauge pressure canner), set a timer and process pint jars for 65 minutes and quart jars for 90 minutes at altitudes of less than 1,000 ft.
Regulate the heat as needed to maintain a steady pressure, and adjust altitude if necessary (see chart below).
When the processing time is complete, turn off the heat, and let the pressure canner cool down to 0 pressure. Once the canner is depressurized, let the canner cool additional 10 minutes before removing the lid.
Spread a dry towel on the counter, unlock the cover, and remove it by tilting the lid 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. If the jars are still boiling vigorously, let them sit in the canner for another 5 minutes or until the boiling slows.
Use the jar lifter to lift jars carefully from the canner and place them on the towel. Keep the jars upright, and don't tighten bands or check the seals yet. Let the jars sit undisturbed for 12 to 24 hours to cool.
After 12 to 24 hours, check to be sure jar lids have sealed by pushing on the center. The cover should not pop up. The jar failed to seal if the lid flexes up and down. Refrigerate the jar and use it up within a few days.
Remove the ring bands, wash, label, date, and store the jars in a cool, dark location (50 to 70 degrees F). Use within 18 months for the best quality—yields about 8 pints or 4 quarts.