Anywhere in Pakistan is classified as extreme condition, so stick to 30,000 kms drain and fill. changing the filter on the 3rd. I recently did a drain and fill on a toyota tacoma (hilux) 2GR.
The total fill is about 8 litres, if you drain the sump and fill it back (same big bolt) it takes 1.5 litres. Hopeless by all regards. OTOH by MB takes 8 litres of ATF, during change and fill it takes 7 litres - well thought out.
The draining of the CVTF from the plastic funnel is good enough, you have to pour about half to one litre and let it drain, it pushes out the old oil. but if you prefer to change the filter every single time its your car, the problem usually is on the hands of the mechanic who can overtighten and warp the sump.
You can go complete flushing and drain from the cooler lines. it would take about 2 gallons - but you would have brand new fluid everywhere.