Just got done with a 20g water change on the 135g setup. It is the first one that I have ever done on it. Since my old RO/DI unit wasn't making water fast, I couldn't do water changes. Now with the new 75gpd unit running, I have plenty of spare water around for water changes. Already have another 20g heating up for the next water change that I want to complete tomorrow evening.
Must be a better way of doing water changes. I took the water from the main tank and replaced the water into the main tank. Got thinking that I should just remove the water from the sump and then replace the water into the sump.
I do have the 20g container on wheels so I can roll it around. Should place the container about the sump and when it ready for a water change I can just dump the water into the sump.
Well anyways, my first water change is done. 
Now I need to complete a water change on the 65g.
135g Main Tank/ 125g Frag tank with 55g sump.