Prius CVT Hybrid Tansaxle Maintenance Problems

[avensus5]

I have a 2004 NHW20 Prius. I note on the Owners Manual (Page 238) on the view of the "Engine compartment overview" (Item4) is a Inverter Reservoir Tank. I suspect that the previous owner has placed water or engine coolant into this reservoir tank. This obviously has grave concerns for me as this may have caused serious damage to the inverter/hybrid transaxle. The owners manual does not specify what goes into this reservoir. Is it ATF WS Toyota brand auto transmission fluid ? or engine LLC coolant ? As there is no dispstick for the CVT Hybrid transmission, how does one check the level ? How does one refilll the CVT fluid (note I have located the drain plug) if there is no dipstick fluid entry point ? i.e., if the Inverter Reservoir Tank is not used for this purpose. Also, if I do not have access to genuine Toyota ATF WS fluid, what other brands (also not indicated in Owners Manual) will suit the Prius ? [Note that this Inverter reservoir tank is not the same as the engine coolant LLC reservoir at the front of the car]. Any assistance for a Prius newbie would be most appreciated.

[statultra]

The inverter resovoir tank uses Super LLC coolant, it flows through a radiator unlike the hybrid transaxle which uses ATF WS.