To see all your sources in Pool, including Screeners, CSV Uploads, and Opt-Outs, head to Pool >> Sources. You can delete CSV Uploads and Opt-Out Lists from this page. Screeners can't be deleted as a source, but see below for how to hide screeners from appearing in your Pool.
The Source Dropdown
This is your top-level filtering mechanism in Pool. Think about this dropdown as "where did these people come from?" For example, if you quickly want to see respondents from a single upload, click the source dropdown from the top left, and then type the name of that CSV Upload. Now your Pool will only show members from that sources. You can email, tag, or even save as a segment.
You can then search for the name of your source, like say a name of a single screener, by typing into the Source dropdown. Let's say we typed "phone" to get to the "Phone Interview Screener," and now you would only see responses for that Source.