Mumbai police made the discovery based on information gathered after the arrest of suspects Preeti Elvin Soren and Amit Jaiswal on Saturday, The Times of India reports.
The authorities questioned the pair for several hours before finding Thapar's headless body in the sewage tank of a Georgetown property.
Soren and Amit Jaiswal reportedly admitted to dumping the body a month ago after strangling the actress. They had reportedly thrown Thapar's decapitated head from a bus.
Police officer Shailesh Kumar Yadav told reporters: "We believe it to be Meenakshi Thapar's body on the basis of alleged killers' statement.
"Efforts are on to trace the head which, the accused claim, was severed after the murder to prevent identification of the deceased."
The body has been sent for DNA tests to confirm the identity of the deceased.
Soren and Jaiswal had reportedly attempted to extort Rs 15 lakh from Thapar's parents. Her mother had deposited Rs.60,000 in her daughter's bank account.