Most pumps are of a rubber diaphram design. No impellers. The white plastic bits were probably from where the factory drilled the tanks for plumbing. As mentioned on the forums in other post, try dumping a bag of ice cubes in toilet before leaving a site, they will scrub the black tank and sensors while your driving. If you can then do another flush your sensors should read fine. We try and do this each trip just to keep things "clean" ?
"DON'T FORCE IT - GET A BIGGER HAMMER'
"Paul & Laurie"
2013 Columbus 340 RK
2013 F350 Dually 6.7 Diesel