Detained asylum seeker in Brisbane's Immigration Transit Accommodation is using a bucket to catch rainwater for washing.

Amin Afravi was medevaced to Australia from Manus Island for treatment of mental health issues, arthritis and psoriasis.

Mr Afravi says his psoriasis becomes inflamed when showering with the facilities tap water, he requested access to one of the rain water tanks to gather water but was denied and has relied on a bucket to catch rainwater.