The hippocampus is thought to respond to information that is being maintained in working memory in other areas. Areas that are commonly thought to maintain working memory include prefrontal cortex (reviews: Chai et al 2018 https://doi.org/10.3389/fpsyg.2018.00401) and entorhinal cortex (Fransen 2005; Egorov et al. 2002). For example, some information about recent trajectory comes to the hippocampus from prefrontal cortex via thalamus (Ito et al. 2015 https://www.nature.com/articles/nature14396).
Critically, episodic memory is not a form of working memory. Episodic memory refers to the content of memory, not the duration. Episodic memory storage occurs in different brain areas at different times. The hippocampus is specialized for rapid acquisition of long-term memories. Look up "systems consolidation of memory".
Also to address your discussion with Bryan, the general idea is that working memory is "stored" through mechanisms other than changing synaptic weights. For example, working memory can be "stored" through persistent activity (Sanders, et al. 2013, https://www.jneurosci.org/content/33/2/424.long) or short-term facilitation of synaptic weights (Mongillo, et al., 2008, https://science.sciencemag.org/content/319/5869/1543.abstract). Review here: https://doi.org/10.1016/j.conb.2013.10.008