Most folks would use one that is 150 to 300 gallons. Locate the tank in an area that is shady and cool. Set up an aeration unit or have another pump circulating the water to create splash. Pump the water from your pond into the holding tank until about a foot from the edge of the container. Clean the Filter Clean all filter material other than bead filters by pulling the material out and pressure washing it with the hose.
Filter media comes in many forms.
Regardless of what type it is, you should take the filter apart, clean it and replace any material that is worn out and shredded. If you have a ProBead biofilter you should take the opportunity to perform a power backwash. This can be done by opening the ball valve at the drain located at the base of the filter while performing a regular backwash. Let this run for a couple of minutes then close the valve. The trick to this is to drain as much water out of the pond as you can so the fish have nowhere to run.