Correct. It’s my experience as a sacristan, that that was left up to me - Father trusted me to inspect the linens very carefully.
(as an aside - I loathe when some people shake out the corporal if as part of their duties they set it out on the Altar when setting up for Mass. Yes, it was part of our duties for one particular priest at one place I served at years ago, and saw another helper/sacristan [apparently experienced] do this. I couldn’t believe it, and rushed over to explain why that shouldn’t be done ]
Yes. We can only deal with what the eye can see, so soaking overnight includes the intention to properly and respectfully deal with any particles on the corporals.
I wouldn’t think anything would be recognizable/left after soaking over night, and unless these were inspected again prior to putting through the washing machine (on their own, separate to other personal washing), I can’t see how one would be aware of any ‘left over matter’.
As long as we exercise due care and attention to what we are doing, treat the sacred linens with the care and respect they deserve, I don’t think we would be accountable to the impossible. So examining carefully prior to soaking, disposing of this first rinse water appropriately , (if only one item with this piece of host was also soaked separately which would then allow it to be inspected more carefully) before being soaked in sodium percarbonate - would be all that would be expected of us. If no more found, then it could be soaked, then washed in the usual way.
If some particles were still observed, then it is no longer exclusively the host (being majorly combined with water by soaking in a generous amount of water in the bucket), but I guess depending on the person - if they have a tender conscience (which is completely different to being scrupulous) they could then dispose of this soak water appropriately too. Though I wouldn’t think that was necessary, but for the peace of their conscience I don’t see any harm.
Another thought - if after the first rinse, they inspected the item (assuming one and soaked on its own separately for its first rinse) and found it still hadn’t completely dissolved, then whilst I agree with the statement you quoted from that article, I also see no harm by giving it another “first” rinse, before soaking it in the sodium percarbonate.