No worries. It is just some leftover construction debris from when the RV was manufactured. Mine did the same thing the first few times I dumped the tanks, but now only the usual stuff comes out. When FR is constructing the RV and drilling/cutting through the floor and walls, some of the campers insulation material falls into the drains/tanks.
I live with fear every day, and sometimes she lets me go fishing.
2015 Shamrock 23IKSS
2008 Ford Expedition EL