A connecting piece for a tubing including a first unit and a second unit is provided. The first unit includes a first connecting element for a tubing element and a second connecting part for the second unit. The second connecting element includes a tubular female part for engagement with the second unit and first sealing elements, and the second unit includes a tubular male part with a collar and second sealing elements for cooperating with the first sealing elements. The first and second units further include separator elements. The first sealing elements and the second sealing elements are configured for mutual locking engagement by moving a male part and a female part axially towards each other.