Scrub-a-Dub-Tub
The Scrub-a-Dub Tub was a playset that was big enough for an adult pony to stand and bathe (or shower) in.
Most versions of the Scrub-a-Dub Tub did not come with a pony. However, there was a rare Scrub-a-Dub Tub Gift Pack that came with three ponies: a Sparkle pony, a Merry-Go-Round pony, and a Sweetheart Sister.[1]
Scrub-a-Dub Tub (no pony version)
Scrub a Dub Tub Story
Scrub-A-Dub Tub Giftpack
The text on the box says "Comes with three ponies, tub, and lots of accessories!" and shows Sky Rocket (Sparkle pony), Spring Song, and Flower Bouquet standing on clouds around the Scrub-a-Dub Tub. Sealed versions of the set have been found with Sky Rocket, Spring Song, and Sunny Bunch, not Flower Bouquet, however. The text next to the ponies indicates the set comes with "Merry Go Round Pony", "Sweetheart Sister Pony", and "Sparkle Pony"; perhaps the ponies included were randomly selected from those sets.