Agreed with @tintin1
Toilet acids available locally are too dangerous and if you use it undiluted, then results you can see in damaged Drainage pipelines in Flats of Karachi streets.
These acids are strong enough and they severely damages Drainage lines(Both G.I as well as Cemented as well as PVC) so when they are damaging these materials, they will surely digest metal
Seems economical solution but temporarily...in the long run it will damage metal.