There's a few ways to deal with the recycled/waste water in an aluminum setup (or any other setup which has excess water):
- Send the water to some other process which uses it up instead
- Loop the pipes back into themselves, but if you do that, you really do need to use a VIP Junction, as described by the Pipeline manual (https://satisfactory.wiki.gg/images/Pipeline_Manual.pdf). Those can be finnicky to build and debug, if there's any build weirdness, but technically once it's working it should be solid.
- Loop the pipes back to a totally separate set of machines. Keep the fresh + recycled totally separate, and underclock/overclock to suit

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