Emergency massive water change

Here is a simple way to change about 99% of your tank water without netting out fish for emergency:

1. drain 80% of tank water,
2. fill tank up to 40% mark,
3. drain water to the 20% mark
4. repeat 2 and 3 for 3 times
5. fill up the tank

In this case, you just changed 80+10+5+2.5+1.25=98.75% of your tank water without netting out the fish. If you really want to close to 100%, repeat steps 2 and 3 few more times.

Of course, you have to make sure that the replacement water has the same pH and temp so you don't shock your fish.

Hope you never have to do this but the information can be useful.