Check out www.SteelTank.com They they cover water tanks too. https://www.steeltank.com/FabricatedSteelProducts/FieldErectedTanks/tabid/472/Default.aspx
I realize this is an older thread but thought an little information may be appreciated. UL specification 142 for Aboveground Fuel Storage Tanks no longer recognizes long bolt manways as an acceptable form of Emergency Venting for newly manufactured tanks. An appropriate fitting with Emergency...