Actually, that material contains non-lead tinning metals:
Here's a link to its MSDA:
http://www.oatey.com/msds/SOL250E6_OATEY_NO_95_LEAD_FREE_TINNING_FLUX.pdf
Note that it contains zinc chloride, which is a component of the flux used in acid-core solder. If you use this "flux" for tinning a soldering tip for electronics, be sure to wipe the tip well afterwards. Most important, do not use that material as a soldering flux for electronics.
Edit: I use a Kester Tinning Block (Kester # 51-0000-0005) when my tip needs heavy cleaning. Usually a wet sponge, as mentioned, suffices. The Kester block is sal ammoniac (ammonium chloride). While there are similarities between zinc chloride and ammonium chloride, the latter evaporates completely when heated while the former does not. Both contain chloride, which you woudlwant to wipe off before using to solder electronics.
John