When it comes to using synonyms for the phrase "drain waters," there are a multitude of options available. The term "drainage" is a common replacement, as it refers to the process of water being removed from an area through a system of pipes or channels. Another option is "runoff," which specifically refers to water that runs off of a surface or area and is collected for drainage. Additional synonyms for "drain waters" include "flow out," "empty out," "discharge," and "seep away." Ultimately, the choice of synonym used will depend on the specific context and intended meaning of the phrase.