Combine seeds and sugar in a large glass bowl; cover and chill at least 8 hours.
Transfer mixture to a heavy nonaluminum saucepan; bring to a boil over medium heat. Reduce heat, and simmer 3 minutes.
Pour mixture through a cheesecloth-lined colander; press mixture against sides of colander with the back of a spoon to squeeze out juice. Discard pulp.
Pour juice into a 1-quart sterilized jar; cover with lid, and screw on band. Cool; store in refrigerator up to 2 weeks.