It does have a filter, like itinerant1 showed above, and it was clear. Here’s what I suspect.
I cut a 1.5 inch hole in the top of the water tank last year b4 storage. Why? The ribbed water fill line (not city water) had a big valley between sidewall and tank, preventing any water passage not pressurized like from a hose. I could get tubing on a hose-end past the dip and force water in if available, but there would have been no way to reasonably fill the tank on the rare occasions of just pouring it in, like prolonged dry camping maybe. And the inlet to the tank was down on the side of the tank with limited space, so pouring would have been a challenge.
So, the hole on top. The tank’s under a fold-up bed, so easy access to its top. I put a food grade stopper tightly in the hole. Anyhow, I suspect some plastic shavings fell down and made their way into the water line enough to restrict the flow. The round piece from the drilling I got out. So I may be looking at purging things somehow.
Hope that all makes sense.