As per the National Sample Survey 2018, nearly 60% of urban India relies on On-Site Sanitation (OSS) systems, like septic tanks and leaching pits, for the management of faecal waste. Augmentation of toilet access over the last five years under the Swachh Bharat Mission has only served to entrench this dependence, despite a push for centralized sewerage systems underwritten by schemes like AMRUT in Class I cities during the same period. Notwithstanding their scale and criticality to public health outcomes, OSS systems are poorly regulated and consequently ill-constructed in India. Therefore, it is vital to address the deficiencies in the downstream sanitation service chain beyond the toilet – beginning with the OSS system - to ensure that India meets its targets toward providing ‘Safely Managed Sanitation Services’ under the Sustainable Development Goal 6. The present study is a novel attempt to systematically analyse the state of OSS in urban India through a sample survey of 3000 households and more than 50 key informant-interviews across ten cities in four states. It shows that septic tanks, confused in common parlance and practice for a septic tank system, comprise the majority of all OSS systems at over 90%. However, in meeting household-level preferences, these systems exhibit variations along each of the principal design parameters, which cumulatively result in less than 2% of all surveyed septic tanks meeting the major requirements of the national governing standards. It finds OSS fraught with several compelling needs, including the inefficacy of septic tanks as primary treatment units, the lack of secondary treatment and safe disposal of pathogenic effluent, their delayed maintenance, and the lack of greywater management. In systematically identifying these issues, the report also recommends interventions in design, planning, and governance for safer and more sustainable on-site sanitation.