In a large nonreactive bowl, combine cucumbers, onion and salt. Cover with crushed ice and mix well. Let stand 3 hours. Drain; rinse and drain thoroughly., In a Dutch oven, combine sugar, water, vinegars, mustard seed, celery seed and peppercorns. Bring to a boil, stirring to dissolve sugar. Add cucumber mixture; return to a boil, stirring occasionally. Reduce heat; simmer, uncovered, 4-5 minutes or until heated through., Carefully ladle hot mixture into 4 hot wide-mouth 1-pint jars, leaving 1/2-in. headspace. Add 3 garlic cloves and 1 bay leaf to each jar. Remove air bubbles and, if necessary, adjust headspace by adding hot pickling liquid. Wipe rims. Center lids on jars; screw on bands until fingertip tight. , Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 10 minutes. Remove jars and cool.