The METU round duct connections are normally not water-tight when mounted normally
Water-tightness could be achieved through sealing with Mastic outside and inside the pipe.
The liquid-tightness depends then on the care with which the sealing measures have been carried out, and the working conditions on the construction site.
Vibrations, temperature fluctuations and extreme temperatures can lead to detachment of the mastic and thus to leakage.
For water and oil-tight connections (tightness class ATC1), we recommend the use of the METU-FORM pipe system which has been developed with precisely this purpose in mind.