One of Rampal's followers was also injured yesterday; he has been put on ventilator at a hospital, the police said. The police is yet to record his statement.
Chand Rathi (32) was arrested from the ashram in Mundka area, police said.
During investigation, the police found Mr Rathi, overseeing the cleaning of the septic tank, did not ensure adequate safety precautions were taken, a senior police officer said.
Police were probing whether other people were also present around the septic tank during the incident.
Last evening, Amarjeet (30) and Makhan Lal (27) had descended into the 90-foot-deep tank to clean it, but the toxic gas inside the tank choked their breath.
Mukesh (25) climbed down the tank to rescue them, but he too lost consciousness, according to the police.
A case was registered for culpable homicide not amounting to murder.