COLORADO police are seeking a porta-potty pervert who was found hiding in a sewage tank at a yoga festival.

One female festival-goer was given the shock of her life when she lifted the seat in a portable toilet to discover a man hiding in the waste tank.

The woman was attending the Hanuman Yoga Festival in Boulder, Colorado, when she was caught short and forced to use one of the dreaded plastic loos.

She told police she dashed outside after noticing something moving inside the tank when she lifted the lid.

Believing there might be a person trapped she asked a man who was standing nearby to go in and check.

He confirmed that there was a man covered in a tarpaulin hiding inside the tank.

A few minutes later, he heard the door lock from the inside. A festival security man waited outside for several minutes before the man finally emerged.

According to festival officials, security tried to detain the man but he ran away, covered in faeces.

He is described as an extremely tall and skinny white male, about 20 years old, wearing dark grey sweatpants and no shirt or shoes.

Police are trying to trace the man who is being sought on charges of criminal attempt to make unlawful sexual contact.

One witness told officers he believed the suspect uses the name "Sky", and that he may be a transient.

Originally published as Potty pervert twist at yoga festival