I believe as with any container a compost bin should be able to get emptied. Either with a bucket or a barrel. I am not sure of the substance name that would come out of the container after all the items have been combined.
The reason for this is that i have high quality bins and have come across higher quality compostable material but I do not wish to combine it with the low quality stuff thats already in there and would like to just empty the bins and put my new stuff in them.