He was rumbled after a woman at the yoga camp, where the temporary toilet was in use, spotted something moving inside the tank when she lifted the lid.
The shocked woman asked a man nearby to check. He later told police he also saw someone inside, covered with a tarpaulin.
The door was then locked from the inside but the suspect came out a few minutes later — covered in excrement.
Security guards at the camp in Boulder, Colorado tried to grab him, but he escaped.
He was described as very tall, white and in his 20s, with thin build and short dark hair. He was wearing grey jogging bottoms but no shirt or shoes.
Eyewitnesses said he also had several cuts on his back and legs, and wore leather bracelets on each wrist.