What I suspect is happening on mine... and mabey yours as well... is that there's some moisture in there that is now bering algae that's making the crap in the strainer. I've never dealt with algae before so I'm not sure. All I know is that I fill mine out of the same tanks and buckets as the tractors and the dozer is the only one to have this trouble. We thought at one time that someone had dumped a pile of dirt in the tank but it's been cleaned thouroghly since that time. Mine is also a machine that can sit for months at a time doing nothing.
Just keep in mind that this strainer is a pre-strainer before the lift pump. The lift pump sends fuel across to the micronic filter on that fuel then comes back to the injection pump... so if your filter is empty you have a supply problem before the filter.... Even if it's full... the problem is probably before the filter since the filter is pressurized.