exposure appears enough. i mix a 25 pound bag of rock salt with hot water in my basement wash tub, put a little down the basement toilet too, one flush with the toilet, mix with some hot water in the washtub, leave some salt. go out for day. so salt water remains in line. the worse the clog the better it works.
might do it two days in a row, if things are bad.
honestly i just do it 4 times a year but always in spring right before trees leaves open. maximum root growth occurs at this time
a quart in a couple doses, 15 minutes apart one dose may be all thats needed. dont do mre often than necessary.
theres a chance it might damage china, or steel drain lines but i havent seen it, thats why i recommend flush 15 times when done, so any remaining acid is washed and diluted.
if the toilet is bad anyway what do you have to lose? and many use drain cleaners with much the same risks without a thought...... so dont fret too much.
yes they do but its only good for a toilet trap clog, and doesnt help a sediment toilet