Cleaning dirt out of fresh water tank

Recently, on three separate occasions lately we've had flow issues with our toilet (twice) and sink faucet (once). Taking them apart, I've found small rocks in the inlets to the valves. Removing these and reinstalling the faucet or toilet valve has restored the flow. We got our trailer used, and have always used a filter on any hose into the trailer (filling the tank or connecting to the city water port). Since this seems to keep happening means that these rocks and grit were already in our system. I've looked at the freshwater tank under the trailer and through the rather opaque white plastic it looks like there is some dirt sediment sitting on the bottom of the tank (that area is slightly darker than the rest). We've tried draining the tank, but the bottom of the tank is dished and the drain isn't quite at the low point, so that doesn't work.  We're at a loss. Does anyone have any ideas how to get this dirt out? At this point I'm wondering if we're going to have to take the tank off, which seems like a major hassle. We're open to any suggestions.

I went through the same issue this week end.  The anode disintegrated and left debris in the bottom of the tank.  Camping World has a very nice wand with a bend on the end and a valve to control the flow.  Worked great!! 

Steve

The tank drain is installed on the sidewall. Park the opposite side tire up on some blocks, then flush tank.

How would the debris from the water heater travel to the fresh tank? Those particles would have to flow backwards thru the water pump, thru it's screens, and then all the way to the under-belly tank. I suppose its possible.