"Backs and fill" is a phrase that is often used to describe someone who is indecisive or vacillating. If you are looking for synonyms for this phrase, there are several options available. Some of the most popular alternatives include "wavering," "hesitating," "procrastinating," "uncertain," and "undecided." Other options include "dithering," "vacillating," "shilly-shallying," and "faltering." Each of these words conveys a similar idea to "backs and fill" but may be more appropriate in certain contexts or convey slightly different shades of meaning. Ultimately, the best synonym will depend on the specific situation and the desired tone or emphasis.