I've just added as I fill.
Always have for 30 + years.
Once you do the python type method, you'll never go back to buckets.
Those are for amatures
Or nano tanks.

Just get something that will adapt a thread garden hose to the shower thread/sink thread, draining is easy, outside, toilet, sink drain etc.Some use a powerhead to pump the water outside and up.
Most just let gravity water the lawn, garden etc.

Then you swap the end on the refill shower head and fill the tank up with the right temp water, your hand can feel about 1-2 F or about 1 C difference.


Regards,
Tom Barr