When I make brews for oral consumption, I separate the sludge from the liquid, put it in a pan, add water and vinegar and simmer it for 10 minutes. Then filter out the solids and boil the liquid down.
The resulting liquid is active and can be combined with the rest of the brew.
The dilution / simmer / filtering / boiling down sequence can be repeated, but probably not worth doing it more than twice.
If that's too much work for the amount of plant material brewed, you can put the sludge in a jar every time you brew, and do the above procedure when you have more sludge to process.