cant get fuel to filters after changing both on Cummins 8.1

Welcome to the forums. It would help if you put your rig in your Sig. Not sure Cummins made a 8.1 but they did make a 8.3L. I put both of my filters on dry on my ISL and cycle the key several times for a minute as that's how long my lift pump runs plus my book does not lie. Some filters require a Oring on the threaded portion and some do not. If it stays on the nipple and the filter you put on does not require it you may think it on tight, but the extra space of the Oring you do not need may be letting air in.