Ah interesting. I'm surprised I haven't gotten anyone here who doesn't flush. I suppose I will flush after all but it's still an interesting topic for debate. For instance, what do you think of this quote pulled from a user of another board?

Flushing is a weird term, a few years back it referred to what you did when you had a chemical salt build up mainly in rockwool slabs but also when over using chemical ferts in compost. ie running lots of water through the medium until all the built up fertiliser and crystallised salts were washed away.

Now it seems it also refers to starving plants during the last week or two of flowering. This of course gives an inferior product compared to what each plant is capable of producing within its genetic potential, ie: less psycoactivity and potency, much more CBD and CBN, less THC, less turpenes and finally lower final crop weight.

Some people in the hydro world now think that by running on just water that they can flush out excess chemicals from the plant by some form of reverse osmosis through the roots into the flushing water. Its amazing the myths that grow in the cannabis community.

Outdoors when growing in soil, where cultivated organically it is nearly impossible to remove any nutrients by rain or water running through the soil. It is only with modern farming practices, that huge amounts of chemical salts get flushed/washed from the soil into our water courses/rivers every time it rains. This happens with both chemicals and through the bad practice of slurry spreading.
It is a good point that when growing outdoors naturally, you cannot flush your plants. Ah well, something to talk about at least