The Oblongs (2001)

Milo and his friends crash a party thrown for the Mayor's daughter, Debbie Bledsoe, and they cause the Debbie's new locket to be tossed into the sewer. The zaftig Helga goes after the gift and gets lodged in the pipe, plugging it up like a human cork. The hill people and rescuers work feverishly to rescue... the locket, and leave Helga blocking the main water line -- just one flush away from the great beyond. Helga causes a disruption in the water supply to valley, but the hill people pay no attention -- until their water is cut off too.