Chem-Tainer TC3581IA 300 gal 35" x 81" Vertical Bulk Storage Tank Industrial Series - Manufactured from linear polyethylene in one piece, seamless construction, this tank series is designed for either indoor or outdoor applications. Its flat bottom design provides for easy and cost efficient installation. Tanks come standard with a vented manway. Non-vented and hinged manways are also available. Non-vent manways are recommended for applications where chemical fumes should be vented away from the tank area.