Step 1Thinly slice the tomatoes. Place them in a large bowl. Add enough water to cover and 2 tablespoons of salt. Cover them and let stand overnight in the refrigerator.
Step 2Place the vinegar, sugar, turmeric, allspice, celery seeds, mustard seeds and 2 tablespoons of salt in a very large non-aluminum pan. Drain the tomatoes, then add them to the pan along with the cabbage, onions and peppers. Bring to a boil, reduce the heat and simmer until the vegetables are very soft, 10 to 15 minutes.
Step 3The relish will keep for several weeks refrigerated, otherwise ladle into sterilized jars and can it according to the instructions in the accompanying story.