Spread a kitchen towel on the counter. Use the jar lifter to remove a hot jar from the canner, drain, and place on the towel. Keep the remaining jars in the canner, so they stay warm.
Use your canning funnel and ladle to pack the hot cucumbers and onions loosely into the jar. Ladle the hot brine over the pickles, and maintaining a 1/2 inch headspace.
Run the bubble popper through the jar to release any trapped air bubbles. Make sure all the pickles are submerged under the brine. Remove any that stick out, and adjust the headspace again if needed.
Wipe the rim to remove any residue, center a lid on the jar, and screw on a band until it is fingertip tight. Use your jar lifter to place the jar back into the canner, and repeat with the remaining jars.
Once all the jars are in canner, adjust the water level so it is 2 inches above the jar tops.
Cover the canner and bring to boil over high heat. Once water boils vigorously, continue boiling and process pickles for 10 minutes at altitudes of less than 1,000 feet. Adjust processing time for your altitude if necessary (See Note).
When processing time is complete, turn off heat, remove the cover, and allow the canner to cool down and settle for about 5 minutes.
Spread a dry kitchen towel on the counter. Remove the cover by tilting lid away from you so that steam does not burn your face.
Use the 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. 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 of the lid. The lid should not pop up. If the lid flexes up and down, it did not seal. Refrigerate jar and use up within a week.
Remove the screw on bands and wash the jars. Label and date the jars. Store in a cool, dark location. Allow 4-5 weeks for the pickles to develop their flavor. Use within a year. Yields about 5 pints depending on the size of your cucumbers.