This is a good learning opportunity that can help you be more handy and self-reliant in the future.
1. It takes less than a gallon to winterize a camper. When the first gallon didn't do the job, you should have went out and looked for problems.
2. When handy people discover a leaking city water inlet, they poke something up in there even if they're not sure how it works. There's nothing to lose in that situation. It already doesn't work; you're not going to make it not work worse. Use common sense, start with something blunt. Don't go ramming an ice pick up there like you're trying to murder something.
Don't be afraid to break a few metaphorical eggs in situations like this.
