Managing local package and artifacts repository

I recently found out that my ~/.julia package was taking about 20GB

I deleted the directory, and started afresh

Are there any “best usage” tips for maintaining a lean ~/.julia directory?

This was discussed recently. Try using the gc function in Pkg
As I recall that thread said that gc did not work as efficiently as expected.

help?> ? Pkg.gc

Garbage collect packages that are no longer reachable from any project. Only packages that are tracked by version
are deleted, so no packages that might contain local changes are touched.

I am aware of gc, but it did not reduce the size of the .julia directory. I had a large number of files in the artifacts subdirectory which gc did not remove
For example, when I build a package with BinaryBuilder in a project directory and perform activate . to make sure that everything is installed in the context of this project/directory, and I later want to discard that project - deleting the directory has no effect on the artifacts that are stored in ~/.julia.
What is the proper way to signal to the package manager that a project is deleted and that its related files can be freed?