create_sa_jetpack_filling.js

/*
  For use with KubeJS. Allows for filling jetpacks and tanks via Spouts in Create.
  Also depends on PowerfulJS.
  
  Save this as a startup_script in your KubeJS directory.
  
  Capacity is mapped in a way that is equivalent to manual filling, e.g. each bucket
  fills by 100.0 "units", so a small tank requires 8 buckets to fill, and a large
  tank requires 32 buckets to fill.
  
  You'll also need to create two new fluid tags, `create_sa:jetpack_water` and 
  `create_sa:jetpack_fuel`. Basic versions of the files needed are included, you can
  add these to `kubejs/data/create_sa/tags/fluids` inside your Minecraft game
  directory.
*/

var tanks = [
    {'id': 'create_sa:small_filling_tank', 'type': 'water', 'capacity': 8000},
    {'id': 'create_sa:medium_filling_tank', 'type': 'water', 'capacity': 16000},
    {'id': 'create_sa:large_filling_tank', 'type': 'water', 'capacity': 32000},
    {'id': 'create_sa:small_fueling_tank', 'type': 'fuel', 'capacity': 8000},
    {'id': 'create_sa:medium_fueling_tank', 'type': 'fuel', 'capacity': 16000},
    {'id': 'create_sa:large_fueling_tank', 'type': 'fuel', 'capacity': 32000},
]

var jetpacks = [
    {'id': 'create_sa:andesite_jetpack_chestplate', 'type': 'fuel'},
    {'id': 'create_sa:brass_jetpack_chestplate', 'type': 'both'},
    {'id': 'create_sa:copper_jetpack_chestplate', 'type': 'water'},
]

ItemEvents.modification(event => {
    tanks.forEach((tank) => {
        event.modify(tank['id'], (item) => {
            item.attachCapability(
                CapabilityBuilder.FLUID.customItemStack()
                    .withCapacity(tank['capacity'])
                    .onFill((container, fluid, simulate) => {
                        if (tank['type'] == 'water' && !fluid.hasTag(`create_sa:jetpack_water`)) {
                            return 0
                        } else if (tank['type'] == 'fuel' && !fluid.hasTag(`create_sa:jetpack_fuel`)) {
                            return 0
                        }

                        let nbt = container.getOrCreateTag()
                        let stock = nbt.getDouble('tagStock') * 10.0
                        let amount = fluid.getAmount()

                        if (fluid.hasTag(`create_sa:jetpack_fuel`) && tank['type'] == 'fuel') {
                            // TODO: Strong and weak fuels

                            /* if (fluid.hasTag(`create_sa:weak_jetpack_fuel`)) {
                                amount /= 2
                            } else if (fluid.hasTag(`create_sa:strong_jetpack_fuel`)) {
                                amount *= 2
                            } */
                        }

                        let filled = Math.min(amount, tank['capacity'] - stock)
                        if (!simulate) {
                            nbt.putDouble('tagStock', (stock + filled) / 10.0)
                            container.setNbt(nbt)
                        }
                        return filled
                    })
            )
        })
    })

    jetpacks.forEach((jetpack) => {
        event.modify(jetpack['id'], (item) => {
            item.attachCapability(
                CapabilityBuilder.FLUID.customItemStack()
                    .withCapacity(16000)
                    .onFill((container, fluid, simulate) => {
                        let nbtKey = null

                        if ((jetpack['type'] == 'water' || jetpack['type'] == 'both') && fluid.hasTag(`create_sa:jetpack_water`)) {
                            nbtKey = 'tagWater'
                        } else if ((jetpack['type'] == 'fuel' || jetpack['type'] == 'both') && fluid.hasTag(`create_sa:jetpack_fuel`)) {
                            nbtKey = 'tagFuel'
                        } else {
                            return 0
                        }

                        let nbt = container.getOrCreateTag()
                        let stock = nbt.getDouble(nbtKey) * 10.0
                        let amount = fluid.getAmount()
                        let filled = Math.min(amount, 16000 - stock)
                        if (!simulate) {
                            nbt.putDouble(nbtKey, (stock + filled) / 10.0)
                            container.setNbt(nbt)
                        }
                        return filled
                    })
            )
        })
    })
})

jetpack_fuel.json

{
    "values": [
        "minecraft:lava"
    ]
}

jetpack_water.json

{
    "values": [
        "minecraft:water"
    ]
}

Hey sorry, looks like that instruction wasn't particularly clear. The folder doesn't need "directory" in the name. Try renaming "fluids directory" to just "fluids" and restart, see if that works.

men ty so much it work perfectly fine, that's so much better