Pick Your Poison is the 17th level of Change is Good. In it, there are three Converters, each for a different fluid (Water, Poison Water, and Toxic Ooze). It focuses on the use of the three to clear a path and fill Swampy's bathtub.
Separate the water into three groups; the smallest over the Toxic Ooze pipe, the middle one over the Poison Water pipe, and the largest over the Water pipe. Send Water to the Toxic Ooze pipe to activate the switch and turn the Algae into pipe. Then, send Water to the Poison Water pipe to clear the way off algae. Finally, send water to the Water pipe and open a hole to Swampy's bathtub.