Bulkhead fittings are used as inlets or outlets on aquariums, sumps and overflows - this article discusses how to size one up for your needs.
Parts Fittings/Bulk Heads. Lifegard Aquatics Bulkhead. Always make sure that you have drilled the appropriate size hole to accommodate your bulk head. The rubber bushing always goes on the 'wet' side of the tank or resevoir for a water tight seal. ...