it's a useless product. Save your money next time.
Looks like you grow in soil from recent diaries. You can give water-only at the end if you want. i wouldn't run excess water through the substrate as the plant cannot grow properly without nutrients. Starving it will only slow down growth/ripening during that time. You can let it suck down the soil's remaining nutrients over a week or more, if you want to. saves you a little effort.
But, it is a figment in many people's head that this does anything useful.
Flushing is an extreme thing intended for extreme problems in the rootzone. so, if you got massive toxicities all over or the pH of you substrate has gone nuts, these are times flushing is useful.
Think about an outside grow. Do they recommend flushign the earth? No, because that would be absurd. When you eat a bunch of pasta, do your bones become pasta? no, your body takes the food you eat, strips it down, repurposes it as it builds new molecules needed for cellular growth. Plant is simpler, but what it 'eats' is still processed into different molecules that are used for cellular growth. What constitutes a cell for stem, flower or leaf is consistent. cellulose is always cellulose. the organelles are still all teh same -- because if this stuff was different or volatile in what constructs them, they wouldn't function properly. the plant would die if it could not do this.
AN is a marketing company. they really don't know much about fertilization from what i can see - their ratios, their lack of ph-buffering on their so-called soilless/hydro nutes etc. They are a bumblefuck company with cartoon graphics on that remind me of sugary cereals and their advertising, lol.
you can make AN work, but they split things up into multiple products just so that you spend more money than necessary. The only molecule you have to be extra careful of is Ca becaue it can more easily form a precipitate with S but only at very strong concentrations - not what you typically see in their watered-down offerings. you pay a lot for shipping water-weight.
Anyway, ignore their 40 different 'necessary' products.. keep it simple. well-balanced feed, proper pH and the plant will be happy. You absolutely don't have to flush it if you don't want to and there is nothign wrong with the plant. blind taste tests show people have no clue between flush and unflushed weed. examining the plant material shows the minerals in buds are at no different levels when flushed or not flushed. it's just magic to sell more bullshit.