Hi i want to add the dietpi repository to a rasberrypi os lite install. I can’t seem to find a sources.list for this.
There is no DietPi APT repository (yet). Software (via dietpi-software) is installed either from the Debian/Raspbian repo, official software repos, Git releases or sources, and in a few cases dpkg packages or binaries directly from our server.
Welcome to our community.
Basically DietPi is not an own OS. It’s a set of bash script on top of a Debian base image. In case of Raspberry PI, we use Raspberry OS as base. Means, DietPi is an extremely slim/diet version of Raspberry OS. Software installation follow basically the same installation steps as you would do on plain Raspberry OS.
Correcting you a bit: We don’t use base “images” anymore but the Debian/Raspbian repo and in cases kernel/firmware repositories from SBC manufacturers or Armbian, on top of a debootstrap from scratch 
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