MTA crews will test the plumbing at the Main Street subway station in Flushing Tuesday to pinpoint the source of raw sewage that workers say is seeping onto the trackbed.

Transit officials believe that the problem originates in a sink that's disconnected from drainage pipes, said Paul Fleuranges, a spokesman for New York City Transit.

Subway cleaners dump soiled water and garbage into the sink, which in turn has flowed into the tracks of the No. 7 train, he said. Fleuranges said it was unclear if the pipes carrying waste from the sink became unhinged from the sewer lines, or were meant to drain directly onto the track bed.

Track workers who first alerted supervisors to the problem said the source of the waste is a toilet, not a sink, judging from the smell and appearance of the detritus.

"Nobody's sink smells like that, not even a fish market," a worker said. "It's definitely a toilet."

Fleuranges said if Tuesday's tests determine the leak originates in a toilet, crews will make the appropriate repairs. "If it's not (a sink), then they'll go back," he said of the maintenance crews.