I've got this bulk washing setup, with a output filter on "Can not be washed".

When I threw in some (gray) wool, the white wool wouldn't come out...
Turns out white wool has a recipe to wash into white wool! 😂

The recipe marks all wool washable into white wool, which i'm assuming comes from here?

Either way, it'd be nice if white wool wouldn't be "washable", any more.

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This issue has been closed since it has been inactive for 3 weeks since it was marked as stale.

An annoyance for sure, but for what it's worth, I think you can set advanced filters to filter out specific blocks as well as via category. For example, my blast furnace has a belt-stopping filter of "can be Smelted", but it's also set to automatically let just-smelted stone and iron ingots through, so it doesn't smelt cobblestone all the way into smooth stone or ruin my iron supply by turning it all into some other mod's "refined iron".