Freezing is fine and I've used it as a storage method however in theory it can damage the seal (one of the reasons why manufacturers shy away from suggesting that form of storage).
BTW Freezing inhibits bacterial growth, it doesn't kill much, but that's not an issue here.
To clean the tube get yourself a bike gear cable (the inner metal part). Clean the oil off it and give it a good wash. Wrap a small amount of tissue paper around the end of the cable and slide it into the tube. I've used this method for a few years now and it works very well.