Back flushing water lines?

Well, the water pump seems to be under the bed with no visible access panel. Odd placement for something that can use periodic maintenance!  Oh, well. A trip to our RV service shop will certainly take care of it. Just wish we could have done it ourselves. It needs to be done well so we can get it sold. It is hard to let it go, but backs aren't what they used to be for getting the hitch and all done. Thanks for all the suggestions and help!

I got the bathroom faucet cleared of grit so that works now. The toilet still has only a dribble of water coming in. i wonder if the Hood River edition 177 has different placement for the water pump. There are only lines disappearing through the floor when I looked behind the panels under the sink.  No pump or bowl. I am surprised that none of the info that came with the trailer shows placement of the water pump. there has got to be a way  to clear the toilet line! 

Ok, on our 177 the water pump is located on the floor, to access it you have to take out 4 tiny screws (we have since replaced them with 2 plastic fingers for quick access) on the panel below the sink, the panel is about 18.5" x  8.5".  Anyway there is enough room to see the pump to your left and find the little plastic bowl.  Also, make sure your slide is out, that way you only have to reach less than a foot to get to the water pump.

As TT mentioned above, check out the water screen by your water pump.  Ours looks like a small plastic bowl that you can see through with a screen just above it, pretty easy to access under the sink and should not be too difficult to unscrew by hand.  You will need a flashlight or use the light on your smartphone to see its location.