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Hello and welcome. Thank you for requesting me. Doing this is a risky project for several reasons. It's difficult to keep enough oxygen in the water of the holding tanks, especially if the weather is hot. Being netted and moved around is stressful to the fish, causing them to need even more oxygen. That being said, you'll need to put water that is the same temperature as what is in the pond in the largest containers you can find. The plastic wading pool for children work well. Large RubberMaid totes also work. If your water source contains chlorine, be sure to use a dechlorinator. Net the fish as gently as possible, one at a time. Sometimes larger koi will bleed from the gills when netted. The bleeding usually stops quickly, and no harm is done. I just wanted you to be aware of that possibility. The biggest danger to your fish occurs after you return them to the clean pond. Removing all the water at once means it is the same as starting with a new pond. Most of the beneficial bacteria will be destroyed. The pond will not be cycled anymore. Ammonia and nitrites can rise, and oxygen decrease. This is a situation where we often see the fish get sick within two weeks of the pond cleaning. For that reason, it's better to do partial water changes regularly, and never remove all of the water at once. I realize you probably have a good reason for wanting to drain and clean the pond, but I wanted to be sure you know about all the possibilities. If you have more questions, let me know in a reply. I wish you success with the pond cleaning.