Odor free, leakproof design made of 100% 3/8" wall virgin polyethylene.Top mounted hose connections eliminate sewage standing in discharge hose which is the major cause of odor permeation through the hose. Raised vacuum relief valve with easy clean screw cap prevents tank collapsing from dock pumpouts with high levels of vacuum and clogged tank vents. Trioinic Super Premium Tanks include the following fittings: 1/2 NPT x 5/8 barb vent assembly, inspection port, 1-1/2" inlet, 1-1/2" outlet (pumpout), vacuum relief valve. **Inlet, outlet and vent fittings can be rotated. Optional overboard discharge available for $30 additional charge. Trionic holding tanks comply with U. S. Coast Guard requirements.