Some manufacturer instructions distinguish hot water draining through an idle appliance from the cold water required during grinding. Check that distinction in your model's manual before adopting a blanket rule.
What the observation tells you
Permission for ordinary hot washing-up water is not permission to grind grease with hot water or pour a kettle into the opening. Temperature limits and connected pipe materials also matter. A newly leaking outlet after hot water needs assessment rather than an assumption that every seal should tolerate it.
A useful next step
Keep fats out, use the specified water for grinding, and seek model-specific guidance if your instructions do not address hot discharge.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.