I do a 25 gal water change on my 135 every two weeks. It takes approx 5 hours to fill a 35 gallon pail with 25gal. of ro/di water. The water change itself takes 12 minutes. Tips? first I use Red Sea Salt, which dissolves almost instantly, and is ready to use in 15 minutes, so, I don't have to make it days ahead. Fill, mix and change in the same day. Second, I attached a magnet to a float valve for the filling bucket and have it set at the 25 gal mark. Third, The first time I did a 25 gal change, I shut off all pumps and power-heads and accurately marked the tank itself with tape to indicate the 25gal level. (have the same at the 10 gal interval). After that first time, now that the tank is marked, I can drain the old water directly into my slop sink, so I do not have to empty the water into a container and then into a drain. Four, (this might be most important) at the end of my 10ft section of hose I attached a home-made PVC elbow that extents low enough into the tank and also over the edge of my slop sink so that it cannot accidentally slip off the tank or the edge of the sink. Five, the other end of the hose is attached to a Mag 7, but the choice of pump is up to you. I added a shut off switch between the plug and outlet, so that I can flip a switch to shut off pump, rather that pull the plug out of the wall. The process is as follows: shut off return pumps and power heads (to get an accurate water level without turbulence).
Hang the Mag 7 with the hose into the tank and flip the switch. No need to start any siphon as the pump does the work. The other end with the elbow hangs over the slop sink. Just watch the water go down in the tank until it reaches the 25 gallon mark on the tank. When mark is reached, shut off switch and quickly remove pump from tank (otherwise it will continue to siphon.) Now take the Mag & and place it directly into the pail containing the newly mixed salt water, put the elbow end over the edge of the tank and flip the switch. 6 minutes for the water to drain, 6 minutes for the tank to fill. Use whatever method you like to mix the salt (pump or manual mixing). The only other step might be a heater for the new water while it is filling (usually only needed in winter) so that there is not such a disparity in temperature when refilling. But I have found that it usually wont drop the temp more that a degree or two anyway. the tank heater quickly takes care of that. Yes the proximity of my sink greatly helps the process as I only need 10ft of hose.