Do you have a Trident?^^^ The lines are very small diameter and for a reason. Means doesn't have to use much tank water to prime and does not need the volume of an inline filter.
Take off the input line and try to blow through it. If you can't, its blocked. Cut it in half, find the half that works. Hopefully it's long enough.
If not need new line.
Have it sample from a clean place.