I only use a small tupperware container of sand for fish that require sand for sleeping, otherwise it's bare bottom with some PVC pipes for places to hide.
After I need to remove a med, I do a large water change and then run ROX 0.8 carbon in a bag for a few days.
When I need to remove copper, I do a 100% water change, rinse with RODI and let the tank dry. Copper is the last step before the DT, and I use a separate temporary holding aquarium for up to a week until they're moved into the DT.
I wouldn't keep sand or rock in a QT at all, it just makes adding the correct dosages of medications harder.