I don't normally recommend scrubbing the rock unless you have several bins with saltwater to scrub them in and be able to rinse numerous times. Because cyano
attaches like crazy. However, you mentioned that you don't want to break down or take out rock. I don't normally suggest to scrub a rock inside the DT but if you absolutely have to you may want to have a buddy there to help scrub while you siphon it out. That way the cyano
is controlled. You may want to turn off your pumps that way it doesn't go all over the place. I would use the siphon without the attachment to get those stubborn spots on the rock. Usually, it will siphon out if you put it directly under the siphon. Good luck!!! Remember to keep up with your water changes! It is key to keeping the water pristine! Hope this helps.