Spread a kitchen towel on the counter. Use your jar lifter to remove warm jars from the canner, drain, and line up on the towel.
Add 1/4 teaspoon of citric acid or 1 tablespoon of bottled lemon juice to each pint sized jar. (Add 1/2-teaspoon citric acid or 2 tablespoons lemon juice to each quart sized jar.)
Use the canning funnel and ladle, and fill the warm jars with hot tomatoes leaving 1/2-inch headspace.
Run the bubble popper through the jars to release air bubbles. Wipe the rims. Use the magnetic lid lifter to lift lids out of the warm water, center lid on the jar, and screw on band until it is fingertip tight.
Use the jar lifter to place jars into the canner leaving space in between them. Once jars are all in canner, adjust the water level so it is at least one inch above the jar tops. Add more hot water if needed so the water level is 2-inches above the jar tops. When adding water, pour the water in between the jars and not directly onto them. Use the hot water from the small pot your lids were in.
Cover the canner and bring to boil over high heat. Once water boils vigorously, process pint sized jars for 35 minutes (quart sized jars for 45 minutes) at altitudes of less than 1,000 ft. Adjust processing time for your altitude if necessary - See notes.
When processing time is complete, turn off heat, remove the cover by tilting lid away from you so that steam does not burn your face, and allow the canner to cool down and settle for 5 minutes.
Spread a kitchen towel on the counter. Use a jar lifter to remove the jars one at a time from the canner. Keep the jars upright, and place them on the towel. Do not tighten ring bands or test the seals yet.
Allow the jars to cool undisturbed for 12 to 24-hours. You should hear the satisfactory "ping" of the jar lids sealing as the jars 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 few days.
Remove the screw on bands and wash the jars. Label, date, and store the jars in a cool, dark place and use within 12 to 18 months. Yields about 9 pint jars of crushed tomatoes.