Abstract: A watershed runoff drainage device is adapted to be used with a drain inlet vault for a storm drain. It includes a funnel member to be inserted into an inlet of the vault for directing substantially all water runoff entering the vault to flow there through prior to entering the vault. A floating hydrocarbon collector is positioned inside or outside the funnel member, and deflectors and other means within the vault inhibit the growth of mosquito larvae and the like within the vault and inhibit any mosquitoes within the vault from escaping the vault.