Snowflake's chance

Following an unscheduled visit to the Health Visitor, we have been equipped with a sample pot and detailed to get a urine sample from Dom. Given that wringing out the morning nappy is apparently unacceptable (both to me and to the doctor), it escapes me as to how we're supposed to do this. The only time he can reliably be expected to do his mannekin pis impression is as he's lowered into a slightly warmer than he'd like bath - not particularly a time, especially as he gets ever more wriggly, when I feel I'm suffering from a surfeit of hands.