Good question.Dealers of course are only dealing for the most part with the same product and fliud on a daily basis.I know its a bladder and when lets say 15 qts added to the machine its apperas to be ALL empted into the trans and final top off is done manualy.The shop I was at added the small can of flush,hooked up machine,rasied auto some and put it in reverse and let idle.More internal pressure in reverse.The machine has a sight glass and you can watch dark fliud flowing through it.Then it shows clean fliud,then none.Turn auto off,unhook machine and doudle check and top off level.It also is flushing coolers and lines of course.Roll machine to the opening for waste oil and insert tube,turn machine on and plurge old fliud into storage tank etc.most auto's/trucks hold 16/17 qts.Some a little more some less.My Mecury Marquis 4.6 held 14.5.My 1998 1500 truck with add on trans cooler held 18 or so.Its great for stuff that the pan is on at weird angles and are prone to leaking after a standard service.WE discounted the total price if it was time for filter AND flush.