Guppy Rescue--Help me pull it off!

[sarcare]

So for thanksgiving I went to a friends house for dinner. She knew I keep fish so she told me I should go see her sister's fish--she thought I'd like it. I went to the basement and tried to find a fish tank, well after some looking I saw a tiny little containor sitting on the desk. It held about two cups of dirty water, a bit of grungy gravel, and a fancy guppy with a tail that was tattered.

This is clearly a fish in need of some help. No heater or filter, and barely any room to turn around. So I want to help save the guppy. My friend told me her sister would kill her if she let anything happen to the guppy, so I'm supposed to come over once her sister returns to try to convince her of the need for better accomadations for her guppy.

So help me figure out a plan for this guppy rescue.

I have a 10g or a 2.5g tank that I can take for her, I have heaters and filters for both. Which size would be best? What is the best procedure for transfering the poor guppy?

 

[Rbishop]

Will the container sit inside the 10 gal? Prepare some new water properly conditioned, and temp adjusted, and slowly add to the old container over several hours, until full, to let the gup adjust? Then set the full container in the 2.5/10, and add prepared water to it until the gup can swim out on its own. Then bring the heater online when the tank is full.