He often treats his wife as a punching bag for his anger.
Tips
usage
出气筒 is purely figurative — there is no literal 'air-vent tube' meaning in modern usage. Pair it with 当作 (dàngzuò, 'treat as') or 找 (zhǎo, 'find'): 找出气筒 ('look for someone to vent at'). Strongly negative — implies undeserved abuse.
memory
出气 = 'let out air/anger', 筒 = 'tube/cylinder'. Picture an inflated balloon you punch to release pressure — that's the metaphor for the unfortunate person on the receiving end.
