I'd suggest using the wet/dry as a sump, but not as origionally intended. If you can't find all the parts of the overflow, go get one and save yourself some headaches. There should be the U-tube, and the part that hangs over the edge of the aquarium, with a slotted intake on one side, and a bulkhead for plumming to connect on the other side.
It seems likely that your neighbor hung onto the pump for the skimmer. If you can't identify the brand and model, check out Skimmer Design 101
to try to figure out what size pump you need for it.
The two best cleaning methods for aquariums are vinegar and or salt scrub. Rinse well after either treatment.
Why arn't you going to use the larger tank and stand?