RV leaking water while filling water tank???

There is a process called plastic welding, I have heard of. It's like taking a soldering iron and swiping across the hole or crack. That's oversimplified, but close. I would check the time fill, for sure,and see if you can find all drain/overflow tubes. I have a low point drain (hot and cold), a fresh water tank drain, and two overflow tubes. Make sure what oughta be closed is, and what oughta not, ain't!