From Anime Bath Scene Wiki
An Inflatable Pool is a small portable Swimming Pool that requires to be filled up by air. It is sometimes used as an improvised Bathtub when there is no bathtub around.
|| Anime Episode or Movie/Manga Chapter
| August 23rd, 1986
|| "Mobile Suit Gundam ZZ episode 25"
|| Elpeo Ple takes a Bubble Bath in an inflatable pool that is pink and rectangle shaped. It was used due to the lack of a real Bathtub being around and brought out specifically for Ple. It is likely that water had to poured manually into the tub and bubble bath had to be added around the same time.