Jill- Interesting project. Depends on how you find the fish (healthy or in need of serious meds) and how far you have to travel. I would do the cautious route and take the fish home in buckets using their tank water. You don't want to shock them with new, pristine water so use at least half a tanks worth of their water to reassemble tank. Keep the filter submerged so the good bacteria survive the trip, and then reassemble the tank with their water plus topping off with new, conditioned water, if needed.
Somehow you want to quarantine these fish before adding them to your tanks. (Or do the reverse method-sacrifice a fish from one of your established tanks by putting him in the 10g. If he lives for two +weeks without any ill effects, then the fish in the new tank are probably ok to add to your tanks. I read this on one of these forums but never tried it). After quarantine just follow the standard drip method: put the fish to be transferred in a container with his water, then slowly add the new tank water over an hours time-then net fish and add to new tank. I"ve learned that no two tanks are the same-my 75g and 10g have different ph levels for instance so I acclimate the fish depending on which tank they are moving into. Good luck with your free find!