Its intended inflow and connection arrangement are part of its design. Adding a basin or shower is not automatically permitted because there is physical space nearby.
What the observation means
A spare-looking connection may have a defined purpose or require a particular product variant. The exact manual determines accepted fixtures.
A useful next step
Identify the unit before planning changes. Do not drill an inlet, adapt a cap or join another waste pipe experimentally. A repair business should confirm the existing arrangement's scope rather than imply that every macerator can serve a complete bathroom.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.