I can not make much of your description. The cut line may just as well be the one you use for winterizing with pink antifreeze, or it may not be.
What is the "main valve"?
Does the water system work at all? If not, what is not working?
I may be ignorant of the systems in an eagle cap, but in the campers I have seen, the only filter was a simple mesh filter next to the pump.
A picture or three may help with understanding. If you don't know how to post one, go to this link and follow instructions there:
http://photoposting.is-great.net
2014 Ford F350 XLT 6.2 SCLB + 2017 Northstar Arrow