You never answered my question as to how the garbage got on Clipperton in the first place.
Most - if not all of it washed ashore. The same for many other islands - like Kure, etc - photo's have been posted that show the debris that ends up on each of these islands - and yes, it also washes up on Heard. The organizers for Clipperton are the same for Heard Island.
I think if you want more details - because you seem to have some kind of concern - contact the leaders of the DX-pedition(s) to Clipperton and Heard and ask them about the actual details of how it will work. I can only vouch that they are genuine, and that's good enough for me.