The 2 fuel filters are inline, after the tank selector valve. If you have problems with a specific tank, the blockage should be at or before the tank selector valve.
When I had fuel delivery problems on my ZD331, I blew air through the line upstream of the first filter, changed the fuel valve, repeat.
It sounds like there may be an obstruction in the tank, or I have heard of a defective valve causing similar symptoms.
As simple as these problems seem, they can be difficult to diagnose and correct. My ZD331 never really ran right (fuel issue) and my solution was to add a secondary lift pump and an additional 2u filter. It's been fine for the past 800 hours.
Sent from my iPad using Tapatalk Pro