Outcome: Unsuccessful. Bath lasted 30 seconds because the plug was immediately dislodged by LTO's bum. Disappointing as I really wanted this to work.
Option 2: In the washing up bowl.
Outcome: Successful - if rather on the small side. Very much helped by the fact it was sunny outside. Don't know what we'll do next year though, or when the weather isn't on our side. Presumably buy a bigger washing up bowl/leave LTO a bit grubby?!