His bucket will probably be dirty but you can line his bucket with a clean garbage bag so the fish are in the bag and the bucket is just keeping the bag in shape. Just make sure the garbage bag does not have any scent or perfumes added to it. Both buckets should have an air stone so that they are being oxygenated. Didn't you have a gang valve for one of the tanks ( or am I thinking of another member on here? ) If you have a gang/splitter valve, use it to add a line to each bucket. If necessary, you can have an open ended air line in one bucket, just set something on top of the line so that the hose doesn't come out of the bucket and you'll have to adjust the valves so both lines are blowing bubbles.