Planted Tank Guru
Join Date: Sep 2004
Location: Garden City, KS
Unless you're getting your plants from grimy sources (like maybe out of a retention pond or something), I don't think you need to worry too much about "cleaning" them. I always put my new plants right directly into the tank, as long as they came from a fish store or another hobbyist.
I suppose you could use your 2.5g as a holding tank, where you can quarantine new plants for a couple of weeks or so while waiting to see if they have diseases or something (not sure what you are concerned about, quite frankly), but then you risk the chance of the plants melting away or something if the conditions in your holding tank are sub-par.
In summary, I think you are being overly paranoid. What exactly are you concerned about new plants bringing with them? I've never had a problem with plants. Back when I first started up my planted tank, I had a problem with a bad batch of cabomba melting away and creating a mess, but it never polluted the water column. It just made a mess, and I had to remove all the stems and do a thorough gravel-vacuum/water change. The tetras I had in there at the time were perfectly fine throughout it all.