Empty sensor pipes

Hello everyone, I am new and the first thing is to send greetings to all, I hope to participate in the forum. I have an Opel Astra 1400 16V of the year 1996, the other day when changing a cooling sleeve, one of the two tubes that go to the vacuum sensor are disconnected and now I am not able to find where it is connected, one of the two goes to the vacuum valve and the other on the back of the engine, someone can help me.