You've kind of skipped some vital info when you left off what year you have but a quick check of the prats catalog here might be a good place to look for info on your water question as Winnebago has done a great job on some Rv by posting a really full blown parts setup where we can do a "superman" type look at things and zoom or turn things over, specify what system we want to see and really drill down to the fine points.
https://catalog3d.winnebagoind.com/menu/Parts.htm
I chose one year at random and it might/might not be the same as what you have but two things do jump out and it might help you sort the question as there are two items which appear to drain from each end of the tank as well as a large 1 1/4 inch drain on the bottom.
So IF this were your year and you find water going out the sides, one might guess it is overflow but if it is simply gushing out the bottom the tank drain might be open?
Top view and bottom but not necessarily your year?
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Richard
Why no RV year, make and floorplan on MY signature as we suggest for others?
I currently DO NOT have one!