draining system

[westie1961]

hi all. having new bathroom fitted, whats the best way to drain down the system?

i was going to tie up the ball cock on the cold water supply tank in the loft then run the hot / cold taps until water stopped.

i have been advised that there should be a 22mm pipe with a shut off valve that isolates the water in the tank but i cant see one.
there is a 15mm pipe at the bottom of the tank with a shut off valve but the valve is coroded and the tap has snapped off, so i dont want to push my luck and the thing break.

would the 22mm pipe with valve be at the top or bottom of the tank.

its a gravity fed system approx 12 years old.

also when using flexible tap connectors would you use ones with compression fittings or push fit?
i was going to get ones with shut off valve buildt into them.

cheers