There are various synonyms for the phrase "set the rubbish alight." One of the most common is "burn the trash," which implies that the garbage is being consumed by fire. Another potential synonym is "ignite the refuse," which highlights the act of starting the fire. A third option is "incinerate the junk," which connotes the use of an industrial facility rather than an open flame. Other synonyms might include "torch the waste," "kindle the litter," or "fire up the debris." Ultimately, the specific synonym chosen will depend on the context and the desired tone of the writing or speech.