It's coming from somewhere and we can't spot where? YUP! Normal head scratcher!
But Winnebago has come through with a great helper for looking through those walls to see what "might" leak.
This is the one I use most often to get a look without having to crawl around for an hour:
Would I be a fussy "XXXXX" to ask what serial number you have? Sometimes that is needed to get down to exactly which build , early or late, so I'll let you choose! I've been called a jerk for asking that question!
But the info you can get is so helpful, I still recommend it to folks!
One build of your RV shows this for black tank top:
There are only a couple suspects for leaks at the tank top and tanks have water at the bottom to freeze, so not likely to crack at top.
But the one that can throw us is where a supply line passes over the tank to drip off looking like a tank leak!
So you have to look at the fresh water lines in that area?
Maybe like this stool supply that "might" be right over the black tank?
Hard to actually relate fresh and drain drawings when on seperate places but this idea may help.
DO keep in mind that this may not be the build for being exactly right for your RV ( I DID NOT ask for the serial number!
I play in that drawing group a lot so, I might pass some hints along if you are having trouble spotting things or moving around in it!
Before zooming we can pick a point on the drawing to keep centered as we click and drag to turn, scroll to zoom, or change the view from front, back, top, left, right. Click on X symbol before zooming, then click on the part you want to keep centered!
Click on item in drawing to highlight in yellow on parts list or the other way to click on list to highlight in yellow on drawing. Clicking repeatedly on part in list will make it flash yellow to help spot small parts we can't find!