Can I use Danco waterproof grease sold for plumbing and faucets to lube seat posts and pedal threads?
As long as there are no carbon fiber parts involved you should be fine. Carbon parts require a special compound, regular grease makes the mating surfaces slippery. That requires applying excessive clamping force which can damage the carbon parts. The grease you have should prevent any oxidation between the seat tube and the seat post.