Hello Retro, Sūdana
means cleaning. See Visuddhimagga XI, 125 note 46 to this verse:
That is how this benefit of the development of concentration is fivefold as a blissful abiding here and now, and so on.
So wise men fail not in devotion
To the pursuit of concentration:
It cleans defiling of stains' pollution,[note 46]
And brings rewards past calculation.
It says an alternative reading here is Sodhana:Sodhana
(nt.) [fr. sodheti] cleansing Vism 276 (as f. ˚nā); examining J i.292; payment (see uddhāra) J i.321.http://dsal.uchicago.edu/cgi-bin/philol ... ali.271246