Drain, or suck and fill gearbox?

[AlanS]

I am ready to 'drain and fill' my 2006 XC70 tranny. I went to Toyota and bought enough Toyota IV fluid. Could I 'suck' and fill instead? I have a MitiVac which I used to use to change my oil in my Mercedes. Is there any advantage to getting under the car and draining vs. sucking out the old fluid via the gearbox dipstick?
If you all prefer that I 'drain'....is there any mistaking the drain plug for any other bolt head on the gearbox. I read somewhere that there is a bolt head that looks similar and, if loosened, is costly...

[oragex]

The bolt mistake is about a bolt that looks like a refill bolt (which is not) and that's located on the upper part of the box. There is no refill bolt on this box, refilling is done via dip stick tube.

Sucking via dip stick tube gets out only 2L (2qts).

The drain bolt is located on the lower part. Draining will remove 3-4L.