Welcome to the forum.
I don,t re-use run off fert/water because as you flush the pots the built up salts will gradually increase.
Run normal water through the pots first , empty the res(tip the pot) & then use the fert/water.
Flushing the pots should only need to be done once a month , doing more won,t do any harm .
Remember to fert very lightly in s/h , if you use 1/2 strength for bark mixes then use 1/4 to 1/8 strength for s/h.