Question about Bosch Hausgeräte WTXH7E50CH

As others say, connect the tube. But there's also a small black rubber plug on the bottom of the tank that you also need to pull out.
There's a holder for this on the top, although it's very easy to lose the rubber plug from there.

This is easy to miss, the professionals installed the machine for us didn't know about it either, so I had to figure it out later.

Simply attach the hose, this is very easy. But don't be alarmed, because the tank fills up anyway. This is deliberate and not a mistake

There are various options. Either connect the hose or via the collection tank at the top. This is well described in the operating instructions (available online).