A trap assembly for draining waste water toward sewer pipes while blocking back flow of odors comprising: a sealant liquid and a waste water, a liquid trap (101; 305) that uses gravity to keep a residual amount of liquid in the trap and allows free flow from an inlet side to an outlet side of the trap, said trap (101;305) containing said waste water and said sealant liquid, wherein the specific density of said sealant liquid is lower than the specific density of said waste water such that said sealant liquid floats above said waste water, and wherein said liquid trap has an interior, a receiving opening for receiving said waste water, an outlet pipe for connecting to a sewer line, and a release opening (124; 332) near a bottom of said interior, wherein said interior further comprises a first compartment and a second compartment (106; 330), wherein said first compartment and said second compartment (106; 330) are connected through at least one relief hole, and wherein said first compartment is connected to said sewer line through outlet pipe, and a valve (122; 220; 336) mounted within said interior in proximity of said release opening (124; 332), said valve (122; 220; 336) configured to occlude said release opening (124; 332) when the buoyancy resulting from said sealant liquid and said waste water in said interior is below a predetermined level, and wherein said valve (122; 220; 336) is in an open position when the buoyancy resulting from said sealant liquid and said waste water is at least equal to said predetermined level, characterized in that said release opening (124; 332) is at the bottom of said second compartment (106; 330), and a release pipe connects said release opening (124; 332) to said sewer line. a sealant liquid and a waste water, a liquid trap (101; 305) that uses gravity to keep a residual amount of liquid in the trap and allows free flow from an inlet side to an outlet side of the trap, said trap (101;305) containing said waste water and said sealant liquid, wherein the specific density of said sealant liquid is lower than the specific density of said waste water such that said sealant liquid floats above said waste water, and wherein said liquid trap has an interior, a receiving opening for receiving said waste water, an outlet pipe for connecting to a sewer line, and a release opening (124; 332) near a bottom of said interior, wherein said interior further comprises a first compartment and a second compartment (106; 330), wherein said first compartment and said second compartment (106; 330) are connected through at least one relief hole, and wherein said first compartment is connected to said sewer line through outlet pipe, and a valve (122; 220; 336) mounted within said interior in proximity of said release opening (124; 332), said valve (122; 220; 336) configured to occlude said release opening (124; 332) when the buoyancy resulting from said sealant liquid and said waste water in said interior is below a predetermined level, and wherein said valve (122; 220; 336) is in an open position when the buoyancy resulting from said sealant liquid and said waste water is at least equal to said predetermined level, characterized in that said release opening (124; 332) is at the bottom of said second compartment (106; 330), and a release pipe connects said release opening (124; 332) to said sewer line.