Instead of using plumbers putty between the sink and the lip of the drain baskets, they used silicon gel.

All the plumbing in our camper is plastic, and all joints are glued, presumedly to resist vibration when the camper moves. The only way to get any parts out is with a saw.

When the drain fitting leaked, the gasket they'd used was too hard to compress with the plastic nut used. I made do with dripping candle wax around the rim and the "sweating it in" gently with a propane torch. I wouldn't recommend the method in a house, since proper repairs aren't really that difficult; but in the camper it's held just fine for a little over 4 years so far. And I've got another candle.

If the nuts holding your parts "bottom" and won't tighten, it's likely that corrosion at the top of where the "loose nuts" were has clogged the threads and you're just running up to the crud. With otherwise good threads a "bigger wrench" can sometimes be applied to force the nut threads through the rust, or you can take the screws out and wire brush vigorously; but neither is really satisfactory. If you "clean up" things, the rust protection will be gone, and future rapid corrosion is a certainty. You might then have to break the screws off to get them out to do it right.

For a temporary fix on the water that "follows the pipe" and misses your bucket, tie a piece of string (or a strip of rag) arond the wet part of the pipe close to the leak and let it hang into a smaller bucket. With a little luck the water will follow the string instead of running down the pipe. If possible use a "wettable" string. Some "plastic rope" is hygrophobic and the water won't follow it as well.

John