Place cucumber slices, red bell pepper, and onion into a large bowl. Mix in salt and celery seed and let the vegetable stand at room temperature for 1 hour, stirring occasionally. Mix sugar and vinegar in a bowl, stirring until the sugar dissolves, and pour the mixture into the vegetables. Stir again.

Spoon the pickles into the canning jars and pour any excess liquid over the pickles. Cover the jars with lids and rings. Refrigerate at least 24 hours; pickles will keep in refrigerator for 3 weeks.