VW diesel mechanics used to fill the new fuel filter with ATF before installing it (but if and only if they were working with a warmed-up motor for easy starting). Not only did the ATF prime the system, but the first rush of full strength ATF would do a great job of cleaning the injectors and the normal cycle of operation of the injection pump quickly thinned the ATF in the filter with #2 from the tank and sent most of the ATF back to the tank where it became just a good quality lubricity and detergent additive. Note, however, that VW doesn't recommend this practice for more recent TDI type motors, and I suspect that the most recent grades of ATF have too high a flashpoint and too much metallic extreme pressure additive for this to be beneficial.