Wow I just discovered this thread. I have been doing this for a few years now. I will have my skimmer overflowing the whole time I am siphoning the tank out and by the time I have taken out about 20 or so gallons of water my skimmer has filled up a 5 gallon bucket or 2 to add to the water change. Glad Im not the only one that does a water change with the skimmer LOL
I plan to wet skim soon so that I am doing almost continuous water changes through out the week. I will still do a water change a few times a month so I can siphon the bottom of the tank out. What I plan to do is have two 5 gallon buckets, one inside the other. I have the bottom bucket drilled in the bottom with a bulkhead and a pipe that goes out and up to about half the height of the bucket and then drains into my return section of the sump. I have the bucket filled about to the same height as the exit pipe with fresh saltwater. I then have a second 5 gallon bucket floating inside that bucket that my skimmers collection cup drains into. As the skimmate fills up the top 5 gallon bucket it forces the bottom 5 gallon bucket of fresh saltwater to drain into the sump keeping the water parameters and salinity in check.
Even if this works I will still have my skimmer overflowing during water changes to assist with the siphoning.