The average janitor earns $26,180 a year. But one San Francisco-based janitor has managed to increase that average tenfold. Liang Zhao Zhang, a BART system service worker, raked in over $275,000 in 2015, thanks to overtime pay.

BART spokesperson Alicia Trost confirmed that Zhang made a base salary of $57,945 and $162,050 in overtime pay. Benefits brought him to a total of $276,121.

This is the third year in a row the janitor has made a six-figure salary.

While researchers at Transparent California, the nonprofit that released the 2015 public employee compensation data, call BART's compensation packages outrageous and irresponsible, Zhang isn't the one to blame, according to his employers. He "signs up for every overtime slot that becomes available," Trost tells CNBC. "He is likely working almost every day of the year cleaning our stations."