FW Dip:
Use a deadicated bucket/container for the treatment container. However, if you have a large number of fish to treat, do not overcrowd the container. You can do small groups at a time, changing the water after each group has been treated.
If you are using tap water be sure to add a dechlorinate like AmQuel. Better to use distilled or RO water.
To help reduce shock, match the pH and water temperature of the freshwater to that of the tank water the fish are coming out of.
Add an ammonia buffer to the freshwater. Again, AmQuel.
Place an airstone into the treatment container to help with oxygen gas exchange replenishment.
If when you initially put the fish in the freshwater they stiffen then settle to the bottom on their sides and do not move around for the first 30 seconds or so, wait it out a few seconds...the fish will likley recover quickly. Fish usually upright themselves and start moving around within the first minute. If concerned, you can nudge them a little bit to stimulate movement. If after a couple of minutes they look to be overly stressed, remove them.
3-5 minutes in the bath and back to the tank they go. Sooner if fish are stressed.