Drilling the bottom of the tank is risky, some tank bottoms are tempored. Also if you get a leak do to faulty seal or bulkhead, and your not there to catch it you will loose 100% of the water and fish.
This is why you never see tanks drilled on the bottom without a overflow builtin. The overflow is a backup, that way if the bulkhead or seal failed the overflow would save your tank.
Also I am not saying you would for get but if you ever forgot about this drain while you where doing your wc you could lose all the water.
If you want a best of both worlds do one of the following two options I have set both up and they both work
1: hook a T and ball valve to the output on your canister, this way your canister can pump the water out of the tank.
2: Put a pvc siphon in your tank 1 inch below where you want the water level to drain to, and place a ball valve on this. Once you start the siphon it will be maintained for ever as you don't drain below the intake. All you do is open the valve let it drain and close it when done.
This is just my 2 cents.