A seamless, double-walled sump is disclosed for collecting run-off materials and waste products. The sump includes a primary containment vessel and a secondary vessel, integrally molded into a single seamless unit. The sump includes a plurality of ribs that cooperate with surrounding concrete or other enclosing material to anchor the sump and prevent floating. The sump may also include a fabric outer layer that serves as an interface between the concrete and the sump to prevent corrosion.