A reactor vessel includes a dipleg connecting a tubular syngas collection chamber and a quench chamber. The collection chamber connects to the dipleg via a slag tap having a frusto-conical part starting from the lower end of the collection chamber and diverging to an opening connected to an interior of the dipleg. The slag tap has a first tubular part connected to the opening of the frusto-conical part and extending in the direction of the dipleg. A second tubular part connects to the frusto-conical part or to the tubular part and extends toward the dipleg. The second tubular part is spaced away from the dipleg to provide an annular space having a discharge conduit. The discharge conduit has a discharge opening located to direct water along the inner wall of the dipleg. At least half of the vertical length of the first tubular part extends below the discharge opening.