Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
The washerman in a dream is a man who removes worries. Washing clothes indicates repentance and relief.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
The washerman indicates a knowledgeable man who purifies people from sins.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
The washerman is interpreted as relief. Whoever sees himself wash a garment, his worry will disappear.