My reason for not using the drain plug was this - I measured and marked on my mityvac the 1 quart intervals. Using evacuation, I know exactly how much comes out in a single step, and can quickly determine what needs to go back in. Sometimes I use the plug, sometimes the vac. i generally haven’t found any debris in the pan of a well-maintained transmission. Im so used to not having a drain plug that I often don’t bother looking.