Two-way trap

In an improved drainage system:

• an inlet pipe, an outlet pipe and a general trap disposed between said inlet and outlet pipes, said general trap providing that when filled with water to an equilibrium water level equal to the lowest point of the outlet pipe, air does not freely communicate between the inlet pipe and the outlet pipe, the improvement comprising an auxiliary trap disposed between the inlet pipe and the outlet pipe and having an inlet end operatively attached to the inlet pipe at or above the equilibrium level and an outlet end operatively attached to the outlet pipe below the equilibrium water level, at a location above a bottom of the trap such that if the general trap became blocked, water would flow through the auxiliary trap yet air would not freely communicate between the inlet pipe and the outlet pipe.

Drain trap structure for installation in buildings, comprising:

• an inlet section and an outlet section, the inlet section being disposed in a first predetermined level above the overflow water level defined by the level of the outlet section, and further comprising a trap interconnecting said inlet and outlet sections and having a descending portion connected to the inlet section and an ascending portion connected to the outlet section, the improvement comprising a duct that is branched off the inlet section at or above said first predetermined level and is connected to the ascending portion of the trap at a location above a bottom of the trap so that the uppermost edge portion of the entrance opening of said duct into the ascending portion is disposed in a predetermined level distance below the overflow water level.