[adc]

First..did you check it running, hot and in park? Did you use the dipstick at the driver fender. Its almost not possible for it to be that low unless someone drained it by mistake and then put atf in the engine.

There are issues here and I would guess the Supertech dexron is the least.

 

[adc]

The plan is to eventually drain and fill with Subaru Atf-hp. Is there anyway to drain it all in one go without a machine?

There are any number of threads using the lines connecting with the radiator. I'm too lazy to look for them.