I figure I would share this with you guys as well... I am lazy as a pig so even 10 min water change would be too hard for me!
Anyway, for ease of explanation, in reference to the photo lets first name the "tubs": from the top row, left-to-right is Tub #1, 2, and 3. The bottom row tubs are #4, 5, and 6.
Tube #1 is where the bioballs sits, water from the overflow drains through the flexible PVC
pipe (white) into the bio ball and then into #1. The base of #1 is filled with aragonite for calcium supplement. Then its drained directly into #5.
#4, 5, 6 are connected via PVC
pipes and bulkheads, and the combined holds about 50 gallon which serves as my sump. They are filled with live rocks. The metal halide pendent over #4 are for algae control (I have macro algae in #4).
#2 and #3 are also connected to each other with pipes and bulkheads, and are my holding / mixing tanks. Fresh water from the RO
system automatically fill them up after each water change (there is a float valve to stop water production), and I pre-mix salts in it. There is a water pump inside #2 for water movement / mixing. Under #2 there is a dump valve that can drain the entire content of both #2 and #3 into #6 in about 15 seconds.
Finally, on #6 there is two additional bulkheads, one connected to the external pump which push water back into the main tank, and the other connected to a ball valve (which is normally closed) that connects to a drain pipe, which goes down... the drain!
Therefore, when I need to do water change, assuming the holding tank is filled and salt has been mixed, I would simply:
1. Open the ball valve on #6 and dump the water from the system straigt down the drain.
2. Open the dump valve on #2 and let it refill the water in the sump.