Fluid And Toxic Transportation Y class 2000 & 2001 are Izotomic Industries Inc. droids designed with with sole order of moving toxic chemicals and waste through the facility.

The 2000 series (Green and Yellow) are made with basic components and not much shielding, while the 2001 line (Red and Gray) were equipped with radiation shielding to protect the unit from contamination when transporting highly radioactive liquids.

Even with its upgrades the 2001 and 2000 suffered from a major flaw, the containers on the back of these robots where held under great pressure, and in the event of a sudden shut down the containers could erupt.

Now rouge after III when under, these large synthetics use strong build in pumps to squirt whatever substance their last directive had them carry at anything considered a threat.
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As said above, 2001 F.A.T.T.Ys are resistant to radio waves, thus meaning the damage buff Ray weapons have against machines is not counted. They have an AoE (Area of Effect) attack they use upon death, also mentioned in the above lore.