Hello natasha9, welcome to Airstream Forums. I have found a wealth of information here. So I will try to give you some insight on your leaking plumbing.
My trailer is a year older than yours, and a bit longer. But both trailers have a lot of similarities. I have just finished fixing the same kind of leak you are experiencing. It isn't fun.
The gray plastic plumbing in our trailers is polybutyle. This material and plumbing systems has now been replaced with PEX. Sharkbite fittings are in the category of "push to connect" fittings. They do work good if you have room to work. In our case, there isn't much room.
My 86 Limited developed a plumbing leak just where yours did. I've owned my trailer for 10 years but have never used the low point drains. I bet the fresh water tank is under the floor somewhere close by.
Chapter 1: My leak showed itself the day before our planned trip of course. I dried it, cleaned it with alcohol, and slobbered two part epoxy on the offending valve and joint. My leak was on the 12v
pump circuit, not the city water circuit. It worked! The next morning we hitched up and left.
Chapter 2: My repair held for two years and 10,000 miles. But it started leaking again this summer. I just finished taking the fresh water tank down, and replacing all the polyb plumbing under the floor and to the kitchen sink and from the bathroom. Big job, but no more leaks. I left out the "low point drains" as I am a air pressure blow and then install RV antifreeze winterizer. I never found the drains very effective and don't trust them to get all the water out. But I do trust all the extra joints for the drains to leak someday. Less joints, less leaks.
So try some epoxy and see if you can smear some into the offending leak. And have nightmares about a big plumbing job coming up.
The photo is my leaker with epoxy after I removed it from the trailer. The other photo shows the three valves under the galley cabinet. No room to work.
Maybe you would like to read my thread on how I replumbed this area on my trailer. I left out all the cuss words, honest.