According to the game wiki
this doesn't appear to be the case. With Corruption in single digits (4-8 points or so) so well below Tainted threshold, spending 2+ weeks at the inn to avoid any extra corruption, the Corruption value never went down even a single point. Either it's a bug, or the wiki needs an update?
How Do I Lose Corruption?
That's a harder question. While the player is still Tainted or below*, they will slowly bleed off Corruption over time (~1 pt. per day). (...)
*) "Tainted or below" translates to Corruption of 74 or less
this doesn't appear to be the case. With Corruption in single digits (4-8 points or so) so well below Tainted threshold, spending 2+ weeks at the inn to avoid any extra corruption, the Corruption value never went down even a single point. Either it's a bug, or the wiki needs an update?