A dvanda compound of words denoting those classes of śudrā-s who have not been expelled from the communion of higher classes, is singular.,
Thus, तक्षायस्करम् 'the carpenter and the blacksmith'; रजकतन्तुवायम् 'the washerman and the weaver.'
The word अनिर्वासित means one not expelled (from the dish).
A Sudra who can take food from the dish of a higher class, without permanently defiling that vessel, is called an Anirvasita Sudra.
Why do we say 'not expelled'? Observe चण्डालमृतपाः 'the Chandala and the Mritapa.',