1In a large saucepan, bring 8 cups water to a boil. Add tomatoes, a few at a time; boil for 30 seconds. Drain and immediately place tomatoes in ice water. Drain and pat dry; peel and finely chop. Place in a stockpot. Add onions and peppers.
Place mustard and celery seed on a double thickness of cheesecloth; bring up corners of cloth and tie with string to form a bag. Add spice bag and the remaining ingredients to the pot. Bring to a boil. Reduce heat and simmer, uncovered, for 60-75 minutes or until slightly thickened. Discard spice bag.
Carefully ladle relish into hot 1-pint jars, leaving 1/2-in. headspace. Remove air bubbles; wipe rims and adjust lids. Process in boiling-water canner for 20 minutes. makes10 pints.