First thing do Not pick off the little screen for the air vent on the gravity fill. Jayco does not use it and on the back side it is sealed with a little caulk to keep the water out! All the venting comes from the over flow tube under the TT.
My gravity fill tube also flows uphill, so it leaks a lot of water until I bought a little adaptor to shove into the gravity fill tube.
My recommendation is to go in to the TT and locate where the water enters the TT for the gravity fill port. The trace the hose down to the tank. I fully expect the hose will only be about 2 feet long. Check to see if the hose is kinked or if it goes up hill a lot. Your water pump should be right there also. For winterizing the rig you will need to know where it is at anyways.
You say you are not mechanically inclined, but looking at it you should get a gut feeling if something does not look right. If you are not sure. Take a picture or two and post them, and we can look them over for you.
This is interesting. The first time I used my old 197, I thought I could fill the tank using the city water connection. No workee! I have never used the city water connection, as I have always camped away from civilization, or at a WalMart.
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2012 Jay Feather 197 w/pull-out
1997 GMC Sub 1500 4x4;
or 2015 Ford F150 4x4 SuperCrew EB