The liquid seal according to the present invention consists of a U-tube having one arm connected to the pipe collecting all the gas vented from across the plant and other arm connected to a liquid holder. The implement has a perforated paddle with oppositely deflected upper portions to enhance mixing of the paint. A detection section 7 detects an electrical parameter changing with a change in the intensity of power reflected from the antenna to the amplifier 3, thereby detecting the intensity of the reflected power. The seal is rotated relative to the structure such that the seal at least partially conforms to the surface.