Prepare the water bath by filling the canning pot with water. Turn the burner on high to boil the water.
Wash the jars with very hot, soapy water.
Place 1 tablespoon of lemon juice and 1/2 tsp of canning salt into each jar.
Using the funnel, fill each jar with the tomato sauce, leaving 1/2-inch headspace.
Run the bubble popper through each jar to ensure that the bubbles are removed.
Wipe each jar rim with a clean paper towel.
Place a clean lid on each jar and turn the bands fingertip tight.
Using the jar lifter, place the jars into the boiling water bath.
Place the lid on the water bath and process for 35 minutes.
Turn off the stove and carefully remove the jars from the water bath with the jar lifter.
Place the jars onto a towel lined cutting board to cool.
Leave the jars for 12 hours to cool before checking for the lids to be secured and labeling the jars.
Store in a cool dry place for up to 2 years.