Empty buffer storage tank (heating) - Kago Econom P 600

Hello,
we have bought a house that is currently empty. The heating system is switched off and is to be scrapped as part of the renovation this year.
It is a Kago Diplomat 280 with Econom P 600 buffer tank (600 l). We have already drained the heating system, but the storage tank is still full.
I opened the 3 small red valves, but only the small reservoir has drained. Do I have to go through the large connections at the top? Do I need to connect a separate pump here?
Unfortunately, I have not found a manual for the system.

Regards
Egon

The tanks are usually directly connected to the household water line and are filled from the bottom. There is often also a valve there to drain the water.

That means turning off the water inside the house. Attach a hose at the bottom and then empty the tank into the drain or outside.

I have already opened the valves at the bottom, but very little came out, so I suspect that only the small container has emptied. The storage tank does not have a direct connection to the water supply. There are 2 pipes at the top that lead to the oven. I opened it directly at the oven at the bottom (connected to the green hose in the picture), which caused the radiators to empty.

Then you have to empty it with an additional pump.