yes you can, i've done it. remove the plants/medium from the containers. remove as much of the dirt by hand as you can, trying not to damage too many roots. you will break quite a bit of roots, but don't sweat it. tending to mother plants results in a lot more root loss. get yourself about 3 buckets. buckets that are roomy enough to hold the medium/root-ball, and room to move your arms around a bit. put enough water in each bucket, to completely submerge the dirt/roots. then you just start at bucket one, and start removing the soil by gently moving the roots/soil around in the water. by the third bucket (or however many you use) you can remove almost all of the soil. this is the basic method i used. you can add/subtract steps as you see fit, lol. (you could just use a hose, but i prefer the buckets.)