They may encounter the contents during assessment, so the product and quantity are important safety information. An ordinary blocked system and one containing strong cleaner are different situations.
What the observation means
Do not add another product or try to dilute it through repeated flushing. Keep the original container or label available.
A useful next step
Stop using connected fixtures and explain when the chemical was introduced. Follow appropriate product and manufacturer advice. Accurate disclosure helps plan safe work; it is more useful than trying to clear the chemical before the visit by opening or draining the unit yourself.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.