Radiator Overflow Bottle Cleaner

Someone recently posted the question of how to clean the sludge staining from inside the radiator overflow bottle.  This has always been difficult or impossible but I think I just discovered a good solution.  Last night I removed the bottle and filled it with a 20:1 mixture of Marine Clean; the cleaning prep product for POR-15.  I let it soak overnight and in the morning I simply rinsed it out and voila!  It now looks like a new one!  May not work on T2 kombis.  Individual results may vary.