It is a relevant symptom, but it does not establish a single component diagnosis. The unit and discharge arrangement need assessment.
What the observation means
A valve, obstruction or installation issue can require different work. Opening a discharge connection can release wastewater and is not a normal owner check.
A useful next step
Stop using the affected system and report when and where water returns. Do not remove the elbow, clamp a pipe or add a second valve as an experiment. Let the appropriate professional establish the cause and compatible remedy.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.