The staff of a rubber manufacturing plant noticed murky water following the alarm sounded by the TOC meter placed at the ditch entering the neighbouring watercourse. The valves downstream of the TOC meter used for containing the pollution were closed and a wastewater recovery pump was switched on with return to the plant’s recently modernised pre-treatment station. However, the faulty sealing of these valves resulted in a residual leak of pollutant (a partially biodegradable surfactant) towards the natural environment that was overcome by reinforced pumping of the wastewater. The watercourse was affected, with no fish mortality observed. Apart from the containment valve’s poor sealing, the incident highlighted the poor sealing of the surfactant retention tank, which was leaking from its heating pin. Fluorescein tests were scheduled by the operator to understand how the content of the retention tank could have entered the rainwater network instead of the wastewater network which led to the pre-treatment station.