Drop pan change filters put back pan, if you used rtv let it cure before adding fluid, then add fluid but DO NOT turn on truck. Pick a point in the line past the torque convertor and remove and attach plastic tube, you can see when the dark fluid turns to bright. You need to add a quart at a time and you drain a quart at a time and turn of truck each time. My truck needs to be in nuetral for transmsion flow. This was you get well over 95% of the fluid changed. Check the youtubes for your year and model and look up dyi transmsion flush, watch a couple. Generally speaking full flushes would be somewhere around 1.5-2/5 on the difficulty scale. Some transmsions needs specialized equipment and proceedures, zf tranny's and toyo are prime examples, they boost the difficulty scale near 4 in some cases. I believe transmsion fluid is vitally important to change frequently. One nice thing about group 4/5 fluids is it increases the interval, so you can do it less. Example again is the zf transmsion, the pao based fluid is called a lifetime fluid. Now, is that a joke? Yes, there is no such thing, but it is an example of what a manu has decided to use for lifetime fluids. If you use maxlife and are not inclined to do full flush, they have a cheap pump that will easily pull a gallon out of tranny and you can out back a gallon, everytime you change your engine oil. The real question should be is constantly keeping tranny oil clean a better option then using an expensive high quality base fluid? Now, I am on board with that strategy, and if you want that truck lasting a good long time at high miles, doing quick flushes is likely better then a full flush with redline over time in a light duty vehicle.
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ALEKO BST1017N 12V 5A DC Motor Fuel Oil Diesel Pump with Hose with Handle