Back flushing water lines?

We received the screen/strainer today and put it in. it has to go in upside down to fit. Turns out the dealer replaced the water pump 6 years ago, though the service dept. denied it at first,  and never put the strainer back in. When I talked to the service dept. he insisted that there wasn't supposed to be a strainer there unless we wanted to add one.  I talked to Kate at Forest River warranty office and she said there definitely was one there and to call her back after I talked to the dealer again. Since it has been 6 years, the dealer's service dept said they wouldn't pay to put one in.  It was easy enough to do ourselves, as it turned out, but we will be doing a bad review for Pan Pacific in French Camp, CA!!! 

Yes, I cleared a lot of grit out of the kitchen faucet, caught in the aerator, and a lot in the bathroom cold water faucet, reached through the panel in the wall by the bed, as advised here, then blew air down the pipe behind the toilet to clear that one out. Now with the strainer in place and knowing that we should keep water in the tank to cut down on calcification, hopefully the problem will be taken care of and we can advise whoever buys it how to fix it should the problem come up again. It sounds like others have had the same experience. Easy to fix with all the help and advice from you guys! Saved us $300-$400 at the RV repair shop!