Is a downloaded OS X installer from the App Store tied to my Apple ID? At work I use an iMac which I'm going to have to reset to factory settings after my job ends. Since I only have access to slow, unstable internet, I thought it might save some time to download the El Capitan installer from the App Store in advance and create a bootable installer drive, rather than using internet recovery.

After I (erase the drive and) use the bootable installer to reinstall the operating system, will the resulting installation be associated with my Apple ID in any way? Or more generally, will it have any personal information associated with me? I'd like to leave a completely fresh, un-personalized installation of OS X for whoever is going to use the computer next.
If by reinstall the OS, you simply mean reinstall it and not run first-time setup, the resulting installation will not be associated with you in any way.

If you intend to run first-time setup, obviously do not login with your Apple ID during that process, and of course don't input any personally-identifiable information either.

There is metadata in a receipt file in the installer file itself that is associated with your Apple ID. That is not transferred to the resulting installation, though.