In which episode do Mulder and Scully investigate a deadly suburban black sludge that comes out after sundown?

This is the episode where Mulder and Scully go to suburbia, posing as a married couple, to investigate a deadly black sludge that comes out after sundown. When they arrive at their new home the neighbors frantically get them moved in before sundown. Mulder hypothesizes that the home owner's association president is behind the black sludge and confronts the man telling him that he created this thing and every year he has to renew his vows in the Tibet.