As has been discussed, those without private bathing facilities made reservations to bathe. If one occupied a parlour suite w/ensuite facilities, how did one go about bathing? The same way? Making a reservation w/a bedroom steward(ess)?
Interesting Lester, I remember that the four deluxe suites aboard the Titanic were booked. The Promenade Suites are accounted for and the Strausses most definitely stayed in a C-Deck Suite. Who stayed in the other C-Deck suite if not the Astors?
From where do you remember that the 4 Parlour Suites were booked? - It seems that you have information not known to any other.
Looking at the "Cave List - 3rd Proof" which seems to have been drafted only days before Titanic sailed only B-51/53/55 and part of the starboard Parlour Suite on C-deck [namely C-55/57] show as having occupants.
While it seems that Jack Thayer occupied C-66 as far as I know C-62/64 was not occupied. A recent suggestion is that if B-52/54/56 had been booked that Ismay would likely have occupied the port-side Parlour Suite on C-deck.