We know Raff suffered some "flooding". We know he dismantled the U-bend of his sink. We know Amanda was still fretting about this next morning, as, instead of going off to Gubbio (_sp?) getting a mop from the cottage and taking it back was at the forefront of her mind. Police noticed "a strong smell of bleach" on entering Raff's apartment, even though he had a cleaning lady to do his cleaning, who was instructed not to use bleach. There was a murder most foul that same night. Rags and a pile of used (?) rubber gloves - the surgical kind - were found, together with two new large bottles of ACE, one of which was newly empty(?)
Therefore, the police reasoned, perhaps Raff unscrewed the U-bend to clean up debris from the said murder, and the bleach was to remove any incriminating traces from his flat.
Early reports claimed Raff googled "bleach" in the early hours. If so, perhaps bleach of the oxygen-based type was sought, hence explaining why Amanda left Quintavalle's after it opened without buying anything as the only bleach they sold was ACE.