What makes a "Saltwater" aquarium? Saltwater aquariums are manufactured with a built in overflow box(s). Most Saltwater aquariums use in stand "sump" style filters. These filters can be refugiums, skimmer sumps, wet/dry's or any combination of these styles. The overflows are pre drilled to accept a 1" schedule 40 drain bulkhead(s). They are also drilled to accept our "IRS" (Integrated Return System) plumbing return kit. The body of the aquarium and materials used are the same as all the rest of our acrylic aquariums and filters. If you have any special needs for a custom configuration (larger drain holes etc...) feel free to contact us and we'll see if we can accommodate your request.