Back in the the good old days before the advent of “O”Ring chain and such we use take the chain off, wash it in kero then boil it in a chain grease. But now with modern chains that would not be practical after all the O ring is suppose to keep the dirt out. Spray on chain lube will lube the chain rollers and side plates, sprockets etc, so putting hot water or hot anything else on is rather pointless. To really lube the hole chain you would have to take it off and soak it in something that will get past the O rings to do the job properly.
By using the method 1st mentioned we used to get 2 or 3 seasons out of a chain, that was for motocross but for road-racing we used oil instead grease for odvious reasons.
Jimbo