I'm unable to put Red or Blue Xenomass as a whitelisted/blacklisted item in the Decontrsuction plan, even via inventory selection.

Could you add that, or let me know how you're auto-collecting via another mod?

Quick update, I'm using "Loose Item Cleanup" to handle this.

I am missing the barrel recipe, I'll open another thread for that.

Xenomass isn't an entity that can be deconstructed, it's an item dropped on the ground and can only be "deconstructed" by using the "Item on ground" special filter.

Which barrel recipe are you missing?

Sorry for the delayed response, I don't have the ability to barrel up or empty Toxic Sludge or Pollution. I added the mod to an existing save, unfortunately it didn't unlock the recipe.

I confirmed via scenario editor that un/re-researching fluid handling resolves the issue, but we want achievements enabled, so I'd rather not use the lua command to un/re-research that.

I can upload my save and send it to you if that would help (or send the IP of my server so you can save your own copy / sync mods)

Ah I see now. I'll have to add a migration to fix that in existing saves, apparently. I'll do that this weekend, shouldn't be too difficult

Weirdly enough they did unlock on our server...

I've just uploaded a version that has a migration to unlock barreling recipes for toxic sludge and polluted air. Please try it with this version.