My understanding of stainless steel is that it is an alloy of iron, chromium, and other elements. You passivate the stainless my using acid to remove the iron from the surface, leaving a layer of chromium that is resistant to oxidation.
The chromium layer on your brass drain tube should stay intact unless it is mechanically disrupted. Under it is a layer of brass, which will contain trace amounts of lead. You could "pickle" the brass to remove that lead, which I have done with some fittings for hoses and pumps. The amount of lead available through a scratch in the chromium layer should be vanishingly small. I would be very surprised to find that any other hazardous chemicals are in play in the metal.
I am not a metalurgist, so will readily defer to someone with more expertise. Meanwhile, I will continue to use my four heatsticks with their chrome plated brass pipes.