"Sinking money into" is a phrase that refers to investing a significant amount of money into something, such as a project or a business. However, there are other synonymic expressions that could be used to convey the same meaning. For instance, "pour money into" or "invest heavily in" represent similar alternatives to "sink money into." Additionally, "spend lavishly on" or "splurge on" can also be used in contexts where the speaker is referring to the act of investing a considerable amount of money into something. Overall, there are several ways to express the notion of "sinking money into," and choosing the most appropriate one often depends on the context and the speaker's intended meaning.