I have well water so its not as much of an issue but I still put Prime in at water changes. When doing my 50% change I dose right into the tank while it is filling, no sense complicating things. Unless your water is very bad and absolutely needs to be treated before coming in contact with your fish?
Also, for anyone else who isn't using draining/refilling this way yet do yourself a favor. If your have a drain and water source close enough you can just buy some cheap bulk tubing and save yourself both money and time. A 1" clear length of hose clamps on to my faucet with the aerator removed and I use a 1/4" for draining either into the sink or out the front door into a flower bed now that it's warm enough.
Also, for anyone else who isn't using draining/refilling this way yet do yourself a favor. If your have a drain and water source close enough you can just buy some cheap bulk tubing and save yourself both money and time. A 1" clear length of hose clamps on to my faucet with the aerator removed and I use a 1/4" for draining either into the sink or out the front door into a flower bed now that it's warm enough.