About 6,000 gallons of heating fuel leaked out of a tank in the basement of a New York University-owned housing complex yesterday. It's unclear exactly what caused the oil to spill out of the tank — which is a backup system for heating and hot water in NYU's Washington Square Village development at Bleecker and Mercer streets, according to the Daily News. "We are determined to figure out what caused the spill and resolve it," said university spokesman John Beckman. Residents were not evacuated from the buildings, but some complained of fumes from the fuel in hallways and stairways. "You breathe this stuff in for five minutes, you'll get headaches," said Irish studies professor John Waters, 45, who lives on the sixth floor with his wife and daughter. "This is a disaster."