Place the diced cucumbers, onion, and red bell pepper in a large mixing bowl. Combine with the salt and pour water over the mixture until covered. Let sit for at least 6 hours or overnight.Drain the cucumber mixture in a colander, rinse thoroughly with water, and drain again.
In a large stock pot, add the sugar, vinegar, and spices and bring to a boil. Reduce the heat to medium-low and simmer for 5 minutes. Add the drained cucumber mixture and return to a boil. Reduce the heat to medium-low and simmer, uncovered, for 10 minutes.Ladle the hot relish into sterile jars, leaving 1/4 inch of headspace. Wipe the rims of the jars clean and seal tightly with the lids.Process the jars in a boiling water bath for 10 minutes. Carefully remove the jars and let them sit undisturbed for 24 hours.Sealed jars will store in a cool, dark place for a year. If the seal is broken, the relish will keep in the fridge for a month.This makes about 4 pints.Let the relish sit for at least a week or two before using to give the flavors time to meld.