Using the "Water Cooler" method you basically just take a large water bottle (typical 5 gallon bottle should be good for most medium sized systems)
you can either use the actual water cooler (bought cheaply in most local classified ads) and replace the spring loaded flip faucet with PVC
plumbing or create your own bottle housing with a bucket and PVC
two key factors: bottle must be higher than the tank so this really works best in an "out of sight" sump situation. Also the contianer must be an air tight bottle shape otherwise the "water cooler" affect won't work and all the water will just drain into the sump. IOW, you can just use a bucket unless you find a way to make an air tight seal around the lid.
For larger systems you could find a way to use multiple bottles by splitting up the PVC
plumbing, joining two drains into one outflow pipe is the first thing that comes to mind.
The valve is there for use during water changes. Close the valve, drain your sump for your change, refill, then re-open the valve.
I had an additional thought! If you us an actual water cooler... in those rather hot days you could change the top off bottle for a bottle full of tank water and plug the cooler in, adjust the valve so there is a slow but constant flow of cold water from the bottle and you have a cheap chiller as well!
now... someone needs to build this so I know it works!! lol