How did you wash your big babies?

Okay I know that sounds like a weird question. My baby isn’t necessarily big, but he’s on the not small size. He’s 21.5lbs and 28 inches at 6 months, most of it being in his midsection. He’s not the best sitter still and I really need to wash those crevices at bath time so I want him reclined. Bath seats all sit up or have a weight limit too small for him. What did you do during this stage?