Hi Jim,
Beautiful tank.
I have 3 50G water tanks in the garage (they were used to hold vinegar and were prettyt cheap, bought in San Meteo a long time ago. Stay away from the containers for oil since they will be very difficult to clean). I use one tank to hold RO/DI, one tank for mixing and extra salterwater holder, and the third one for RO/DI water. First container has a pump to pump water into the second one. The second tank has a pump plumped to mix saltwater and/or pump water into the third container. I use two Litermeter III pumps for water change, and they are calibrated to pump out the same amount of water as the water that come in. If you are not familiar with Litermeter, they basically operate 150 times a day to achieve the total amount set to it. Even though the pumps do not operate continously, it is continous enough that people call this continous water change

. As a result, you might loose up to 21% of unused water. To save all the back breaking labor with this little cost, I think it is all worth it. Moreover, it introduces no temperature/chemistry swing since everything is pumped in/out slowly, your fish/coral will not suffer because you get busy and cannot change the water, and you will not mess up your beautiful floor because of the water spill. I think if I did not have the auto water changed, I probably have already burnt myself out by this hobby.
My house have crowspace, so I plumbed everything from garage to the tank udner the house. I used 1/4" lines since this is the line used on the pump under the house. If I was to do it again, I probably will use 3/8" line instead since 1/4" line get clogged by calcium deposit pretty easily, and it is a pain to remember running vinegar every half a year to prevent the lines from clogging.
Tong