Water trap having a rotary valve

A siphon device with a bypass, comprising:

• a siphon upper section with a top coupling means for connecting to a drain outlet, a side drain opening with coupling means for connecting to a wastewater utility pipe, wherein said siphon upper section allows direct flow through said side drain opening, bypassing a basin of said siphon, and evacuating a substantial volume of accumulated water directly into the wastewater utility pipe, wherein the siphon upper section includes a fixed tube with at least one first bypass opening facing the side drain opening and a rotatable tube that is concentric with said fixed tube and comprises at least one second bypass opening, wherein said siphon can be shifted from a closed bypass state, in which the rotatable tube blocks the second bypass opening, to an open bypass state by rotating the rotatable tube towards the fixed tube until the second bypass opening overlaps with the first bypass opening, wherein the fixed tube is located within the rotatable tube.