We are talking about the value of gil, not the value of items. Farming/crafting items then blowing them up does not add or remove any actual gil value to the game. The only items that remove gil from the game, are items purchased with gil via an NPC (which are very few).

An item is farmed by person A, (increasing/decreasing the amount of gil on a server by 0).
Those items are then purchased by person B, so person A gets gil (this is circulation, not adding any gil into the game)
Person B makes Cobalt Hauby and sells it on the market (another example of circulation, no gil is being added or removed).
Person C buys that hauby and blows it up. No gil is removed from the game (aside from market taxes).

This is not a gil sink, as it does not increase or reduce the value of GIL in the game, it simply circulates it.

As for the items I was talking about - I am talking about "Coke" "Aquerius Whetstone" "hardened sap" etc etc