For years I pulled bucket duty while draining and filling tanks. Was not until a couple years ago that I first tried the Python. (came with used tank I purchased) I kick myself
for resisting for so long. It is quite simple to use. Hook it up to the faucet and twist the fitting provided one way to drain,and then whhen ready to fill, twist the fitting the other way. You can adjust the temp of the water while the tank is draining so that when you twist it to refill,, you are not adding too cold or too hot of water.
To add dechlorinator.,, I have marked a piece of scotch tape and stuck it on the side of the aquarium at the level of ten,twenty,or thirty gal however much I removed. Then just before I switch or twist the fitting to refill the tank and after making the water comfortable temp wise,, I simply add a little more dechlorinator than needed for the volume of water I removed directly to the tank and then begin filling.
You can also remove the fitting that goes to faucet and simply drain the old water out the door,window,tub,garden ,etc. This allows you to conserve water and only use the faucet for refilling so as to achieve proper temp. You will like the python and I recommend getting extension hose if tanks are far from the drain. Hope some of this helps.