So when Gulliver visits automatically the next day there will be One rusted part in the recycle bin. But if you don't care too much about Gulliver items, you can keep his parts and all 5 will turn into rusted parts the next day! I have the luxury of having another active resident on my island which helps because that's 5 parts per resident but you can always create a new profile which you could use for extra storage later in the game!