Sounds like you had a lime / calcium scale problem, if Pepis cleared it. Some drain cleaners have hydrochloric acid, which will have similar effect to Pepis, but some what stronger. Well, the old formula Pepis might have been stronger than now days.
Christopher A. Young Learn more about Jesus
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Don't know about the solution, but about using carbonated beverages...
Back in the student days when one was forced to live in accomodations less than one would put up with today; four of us lived in a rented house [to save money it still took all four of us]. The landlord did not really clean up too well after the previous tenants, so we had one upstairs sink that was so clogged with some type of gunk [could be seen looking down through the overflow] it seemed to drain faster with the plug in than with the plug out.
We tried every process we could think of, hot water, pumping, etc, every chemical we could find, including gasoline and paint thinner - after all we were desparate to get this sink cleaned up for use. Absolutely nothing touched the sludgy, ?? gunk.
In an act of frustration and desparation I poured my bottle of Pepis into the overflow. The reaction was incredible. Foaming, billing out, then suddenly 'flump' like sound as everything just went down the drain. I continued to pour the remaining soda down the overflow to watch foaming completely clean the view. Until voila! the sink was totally brought back to original draining operation - fixed!
Plus, much of the metal was shiney again.