What're the specifics of making the toilet at the end? I know you get the cistern, but somehow you can interact with the toilet at quite a distance and use the cistern 3 times to make the toilet. Is it a timing thing or is there something that I am missing?

Yes, the end toilet does not require all three of the specific toilet items in order to finish, it just needs three toilet items. And, for whatever reason, if you interact with the end toilet from a platform or two away, it will assemble the toilet and also return the water tank to your inventory. Rinse and repeat for sweet piss relief. No timing or anything tricky, just pointing and clicking.

@candy clicker said : In many games, you need to interact with the base of the toilet or the designated area where the toilet is to be constructed. This might be a physical interaction or using an in-game menu.