Transmission Drain and Fill

Erm... there's no belt. There's no torque converter either. While we're at it there aren't any clutches, bands or brakes.

I think it's good to change transmission fluid in these... just nowhere near as necessary as with any traditional automatic.

 

There's no torque converter in any of the Toyota Hybrid Transaxles that I know of. There's simply no need, MG1 replaces the need for them.
In all models other than the Aqua/Prius C, the fluid runs through the coolant system, so if you wanna be lazy you can just unplug one end, point it into a bucket, and fill it up using the other, for a total flush. Still, just letting it drain and refilling will get nearly everything in it out.
Additionally, I don't think I've seen a single belt in any of the Aqua's I've torn apart so far, let alone in the transmission.

 

The transaxle fluid runs through the coolant system? i did not knew that the Prius C had that. Are you sure about that?