I have two tanks connected by PVC, a 180, and 125.
One end of the 125 is the filter, a square of Porret foam fits the entire end, with a pump and some bags of bio-media on one side,
so the Porret (and media bags)filter both tanks.
To clean the filter I need to remove the Porret panel, pull off the leaf litter, and flowers etc that have landed in the tank (its outside)
and hose it down.
In the process of removing the 20"x20"x2" block of Porrett, it releases a lot of gunk, so both tanks get clouded up, (can't see thru) it takes about 8 hours to clear.
Even with all that release of gunk in the water, there is still plenty to rinse out, and once the Porrett is hosed down and returned, all the floating gunk helps season the newly rinsed block.
After 8 hours or so, both tanks are back to normal.
The 125 above
180 below
I normally do an approx 30% to 40% water change every other day, so one 60 gal water change takes care of both tanks at once.
To do it, the depth of water in the 125 is taken down by about half, watering the garden with old water, and filling backup with the hose.
Even at 50% down, there is plenty of water over the 1500 gph pump, it is kept up and running during the WC.