Mickey and the Seal (1948)

Mickey visits the zoo, where he makes friends with a baby seal by feeding it a couple of fish from his picnic basket. The seal stows away and goes home with Mickey, where for a while, only Pluto sees it. But it climbs into Mickey's bath, and he eventually figures it out and returns the tot. He tells his elders of the wonders of Mickey's bath and scrub-brush, and Mickey returns home to find a welcoming committee.