Formal — to staff
Onsen · Sento
You
すみません、もしよろしければ、背中を流していただけませんか？
すみません、もしよろしければ、せなかをながしていただけませんか？
Excuse me, if it's okay, could you please wash my back for me?
Romaji: Sumimasen, moshi yoroshikereba, senaka o nagashite itadakemasen ka? / Reply Romaji: Hai, mochiron desu. Douzo.
Reply
はい、もちろんです。どうぞ。
はい、もちろんです。どうぞ。
Yes, of course. Please.
Gesture & etiquette
Polite bow, slight nod, possibly indicating your back with a hand gesture (not pointing).
Do not ask strangers to wash your body in a private or overly intimate way. This phrase is for a brief and practical help with back rinsing, which is sometimes done in public baths among friends or family, but less common with strangers. Be mindful of personal space and accept if they decline. In a public bath, it's usually about rinsing soap off, not scrubbing.