Porcelain tub stained all over by gases from drain cleaner

A. Hi Laura. Sadly, I think it very unlikely to be a residue.

Luck & Regards,

A. I tried a toilet bowl cleaner ⇦ this on eBay or Amazon [affil links] and it worked for me. I think it is called The Works Thick blue toilet bowl cleaner .
Test it first to make sure it won't hurt your tub's surface. Good luck!

A. The Works product mentioned in the answer posted is essentially the same as CLR or Lime-A-Way Toilet Bowl Cleaner [affil links], in case you have trouble finding the works. In my area The Works is carried at Dollar TREE Stores.

A. Why do you think you have a sulfuric acid problem?
A search on Black Swan cleaner says that it is a blend of potassium and sodium hydroxides -- about as far as you can get chemically from sulfuric acid --
http://www.blackswanmfg.com//product-information/46-drain-and-waste-system-cleaners/166-liquid-drain-pipe-opener

Hi Geoff. Black Swan offers both caustic and sulfuric acid based drain cleaners. Here's the corresponding page for the sulfuric acid one --
http://www.blackswanmfg.com//product-information/46-drain-and-waste-system-cleaners/164-zap-drain-pipe-opener
Considering the black color of the deposits, sulfuric acid doesn't sound unlikely.

A. Christine, we have a number of threads about cleaning damage to stainless steel sinks. As for the pots & pans and dishes, can you remove all visible discoloration that would turn you off? Because, if there is any invisible stuff that won't come off in hot water and detergent with scrubbing, it's not likely to come off from contact with food, is it? You can put the dishes in your dishwasher after hand scrubbing, but don't put aluminum pots & pans into a dishwasher.

Regards,

! Hi Ted
Mea culpa. We don't have Black Swan this side of the pond so I did not look further than my first finding.
Has it not occurred to anyone that supplying both strong acid and strong alkali under the same brand name has a potential for considerable trouble.

Indeed Geoff. It isn't hard to picture a homeowner deciding to consolidate two partial bottles of drain cleaner to clear-up their under-counter space. Although I haven't done it with drain cleaner, I've done it with everything else from dish detergent to Maker's Mark.

Regards,

Hi again Christine. I already gave you my answer, but I repeat it here again:

Were you able to get all visible contamination off? If not, what are you seeing that you feel may be dangerous? If you see something specific we can at least guess what it is, what it means, what to do about it, and whether it's a safety issue.

If you see nothing, but you don't accept my logic that this invisible something or nothing is not going to come off accidentally in your food if you can't get it off either by scrubbing or in the dishwasher, then I can't help, sorry. Good luck.

Regards,

A. Since we're talking about metals, a lot of the discoloration that people take to be a "stain" (as in, a residue of foreign material stuck on the surface) is very frequently an etch mark (as in, somebody used a wood rasp on your wooden table that had a smooth sanded finish).

Acids are generally water soluble stuff, so they will leave a residue if the acid solution just sits and evaporates, but will not leave a residue if the acid solution is rinsed off. (And if you do have acid residue, it will usually redissolve if you reintroduce water to it.)

However also, we are talking about cookware, which frequently has some type of coating over the metal surface. It is this coating that your food comes into contact with, not the metal itself. If the acid attack has removed the coating and exposed the metal underneath, then it may become a legitimate question, is the surface as it is now safe for food contact? That being said, no, it's not terribly likely that you're going to see any appreciable metal contamination leeching off a pan over the temperature and time span used for most recipes.