Combine squash, onions, and peppers in large bowl; toss gently. Sprinkle salt over vegetables. Cover and let stand 8 hours. Drain.
Return vegetables to large bowl. Cover with cold water. Let stand 20 minutes. Drain vegetables, well.
Tie pickling spices in cheesecloth bag. Combine pickling spices, vinegar, and turmeric in medium saucepan. Bring to boil. Place sugar in large Dutch oven. Pour boiling mixture over sugar, stirring well. Stir in vegetables. Cook over medium-high heat for 10 minutes. Remove spice bag. Ladle relish into hot sterilized jars, leaving 1/4-inch headspace. Remove air bubbles; wipe jar rims. Cover at once with metal lids, and screw on bands. Store in refrigerator. Yield: 6 pints.