Stockosorb - long term water storage granules - Super absorbent water retaining gel for indoor and outdoor pots - 2x100g

Can you add this product dry to compost or do you have to soak in water ?

I am planning on using this product in some large garden tubs holding 80l of compost which will hold bushes, what is the life span of this product ?

Does this product stay in your soil forever or does it eventually biodegrade?