RE: Low point drain valves replacement
I don't know what size tubing you have, but it looks looks like you used a 3/8" fitting when you need a 1/2" fitting.
RE: weight dist chain replacement
Don't know if they are special or not, but I would think a grade 70 chain in the size need would do, a 5/16" grade 70 chain has a working load limit of 4700#