it is ok to prefill the primary filter (the first one from the tank)
install the secondary filter dry. the common rail fuel systems have a lot closer clearances in the high pres pump and the injectors and that little bit of dirt that may get into the filter when filling it can cause fuel system issues. also if there are clearance issues getting the filter in position to install it is a good idea to cover the filter with a clean cloth until it is in position to install then remove the cloth being carful not to let any dirt that may have fell on it drop into the filter.
