調教…じゃなかった、水泳トレーニング

Breaking her in... uh, I mean, swimming training.

The first word here means "training" in the sense of "training an animal" (and is normally also used for horses), but has a derogatory connotation when applied to a human (i.e. "training someone like an animal"). It also often has sexual connotations because of its use in S&M contexts (and H games).