How long do deleted builds remain available? Will the API allow to immediately remove them?

How long do deleted builds remain available? Will the API allow to immediately remove them?

We transfer our builds to another server when complete and would prefer that our binaries do not stay on a server not under our control. So, we'd like to immedately remove the build and not have it available at all like when you select "show deleted builds". Is this possible? If not how long do the binaries stay on the server? Is there a custom retention policy we can set?