Looking to get second T.Grans

Hi,
I am looking to get a second T.Granulosa especially now after finding out from Ester & others that they seem happier in groups (this is my excuse, but I'm dying to get another). Anyway
I like to quarantine the new edition and was given a good suggestion in a different thread to use a Rubbermaid bin and a prematured sponge filter. Sounds reasonable enough to me but I don't presently have a sponge filter. If I pick one up today how long would it take to premature it? Or can I use some of the water from the already established tank mix it with dechlorinated water and use a sponge filter. How often & how much water should be changed? I have never used a sponge filter or any tank size less than a 10gallon. Also how long should quarantine. I have been reading many threads & I am reading 30 days in some 60 days in others is their any specified time or is it all a matter of opinion & how the new one is eating and behaving. If anyone has other suggestions as to HOW & HOW LONG they quarantined their latest edition please feel free to throw out your method or any suggestions they are welcomed and appreciated. I'm sure everyone has their own method & I'm very interested in as many ideas as possible. If Ester happens to read this, up in the photo gallery you posted a picture of your newt in quarantine "Wishful thinking.. taricha dreams of a better place". What is your set up? It looks interesting. Thanks. Michelle

For quarantine:
I used a 30x30x30cm box, with 2 cm of dirt, a shallow water dish (also 2cm of water). I made sure they ate from tweezers regularly before moving them into the larger setup. In total the shortest stay was 3 weeks, the longest stay was 6 weeks. Once they start eating regularly, their skin looks healthy, no coughing/sneezing type actions are observed I tend to move them.

The main setup:
100 cm x 40 cm x 50 cm. There are a few glued pieces of glass that create a land area (bridge). The water level is approximately 20 cm, there is a cork bark ramp leading out of the water on both sides and a piece of aquarium wood which they can also climb in the center.
The plant I use is a prayer plant, the version that stays close to the ground. This provides hiding spots for the newts when they leave the water.

Thanks Ester.
Does anyone have an opinion of a bin,tank water & dechlorinated water with a new sponge filter?