The ‘Straw Soup’ as I like to call it works very well as a general purpose Herbicide, i use mine on the stone paths around my house to combat weeds and grass growth, excess goes in in the drain as above.
As for the bags, I have heard of people re-using them for the growing process after rinsing with a bleach mixture, the trouble with this though is every re-use the bag gets weaker and will eventually develop small holes on creases that allow contamination.
I did read an interesting study where after the final flush, the bags were moved to an outside area and composting worms were introduced, after the worms had done their business they were moved to a hot house and sweet potato was planted directly in the bag, they were large bags though, approx 5kg of substrate, not appropriate for coffee based substrate in my experience as they struggle to fully colonise without making dozens of pin pricks around the bottom to allow extra gas exchange, which kind of defeats the purpose of using a filter patch bag.
Good Luck!
.
