When you want to express the action of adding something in large quantities, the phrase 'pour in' is frequently used. However, there are various other phrases which can also be used to indicate a similar action. Some common synonyms for 'pour in' include "add," "infuse," "put in," "inject," "incorporate," "introduce," "throw in," "dump," "load," and "fill up." While the meaning of these phrases is equivalent, each has a slightly different tone and a different level of formality. So, you can use the alternative synonym which suits best according to the context and the tone of your writing or speech.