cant get fuel to filters after changing both on Cummins 8.1

Back in high school, I worked in a truck dealership. When they changed filters they would pre-fill them prior to installing. There may be a better way but it worked

Black stuff is Algae and you need to add a bio-side to kill it.

Thanks all for response==all are much appreciated. Now for rest of story. The filters were new about 6000 miles ago however after purchasing fuel in Pa very shortly blinking light came on an so i switched first filter.Engine ran fine afterward.However i cut filter apart when i got home an it was COMPLETELY PLUGGED WITH BLACK GO.
After thinking should i remove both filters an check there condition.This i did an filter i changed was somewhat black but the final filter was very clean.So i dont know if i got bad fuel or if it was just stuff from 6000miles? But i did read Cummins book an it said it should self prime but after an again it said prefilling is recomended. This evening i did that ---turned key --went back an listened to transfer pump an it started with no miss!!!!! I have always been hesitant to remove final filter because long ago on my first CASE farm tractor it was recomended not do that unless necessary as it is last barrier to dirt in injection pump. In the future i will change first filter perhaps every 5000 miles. I did have a plastic plug that i put in center hole to keep dirt out.
So again many thanks for responses.

Sometimes people have to put air in the tank to push fuel up to the filters.

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.

First off the book basically lies. Best option is to plug the center hole and fill the filter with fuel before installing. Cycling the key on for about 20 seconds then off about 10 times may fill the filters. My last experience with this was not good as mine air locked and the only way I could get it to fire up was to pull the return line and plug it off while I cranked the engine as fuel would take the path of least resistance and just go from the tank and back through the return line and never enter the chambers. If it were my rig I would remove the filters fill them and try it. If it still did not start I would plug the return line. Be careful because if you crank the starter too long you will burn it up.