@@masterresad first you must use Toyota WS ATF not any others it a must , second you can not flush the entire fluid on my max 50% called drain and refill the reason behind it is you must leave 50% dirty oil because it contains clutch dust and the clutch dust in the oil makes clutches to bind so do not look that ail is darker it for that reason when you flinch that clutch dust and clutch has none then transition will start to slip . You can only to this then car is completely cold as ATF expends when it warm so you must know how much exactly you got out and refill the same plus a bit more then lastly you must get ATF to 50c and then remove overflowing valve and get all extra oil out so the transmission is very sensitive to oil you use and need to have correct level and never ever flush . Better if you do not touch this transmission at all we designed them to last for 500000 miles on original WS oil so no need to replace it ever. STF is not a motor oil that you must replace every 5k miles ATF is not dirty as you visually see it is darker for a purpose