I think I may have missed on following the line --or confused myself!
Thinking over the suction valve, that did not really fit, so looking again, I think I see the line for the stool and the vanity sink on this one line to the manifold and that may make more sense, if I'm following what you are saying correctly.
Water is working okay in all places except the small sink and stool?
Interactive parts catalog here:
Down to fresh water plumbing here:
Hints on use of this drawing set?
Choose one of the views at bottom right, spot an area you want to see better like the stool line,etc. and click the far bottom,far left symbol like a cross with period in center? Click that and then an item on the drawing and that will keep that item centered as you zoom, move, or turn things to follow the lines!
Scroll to zoom or hold curser on drawing to drag it around.
If you get the RV turned over or get sea sick,----back out and start again!!
It takes sometime to get the feel of it!
Note that you can click on the item and it shows at right for ID or if you know the name of an item, click in the list and it shows yellow on the drawing. That can help when you either don't know what it is called or if you know the name like converter but have no idea where it sets on the RV! Keep clicking on the list and it will flash yellow to spot it on the drawing!
Meanwhile I now think you may have a stoppage where that line comes off the manifold or along that single line that feeds both?
But that may be easier to follow when you can see it while looking at what the drawing shows! Drawings are good but a really good eye ball is better!