Question
I am installing an InSinkErator Badger 5 (1/2 hp) under a double sink. There is no dishwasher. The disposal outlet lines up with the horizontal pipe that feeds a tee, then a single P-trap, then the wall drain. The manual mentions two traps. The disposal also features a 90-degree discharge tube that directs the flow downward. I want to avoid major rework. Can I keep everything horizontal and avoid vertical changes? Are there basic double-sink disposal layouts? Drawings would help.
Answer
You seldom want two traps on a double sink. Use one P-trap serving both bowls through a “continuous waste” kit with a baffle tee. That layout prevents siphoning and is the standard method in many jurisdictions. Mount the Badger 5 on one bowl. Rotate the disposal’s discharge elbow sideways so it aims toward the baffle tee, not straight down. Keep a slight downward slope on the short discharge run. Aim for roughly 1/4 inch per foot. Connect the non-disposal bowl to the other side of the baffle tee. Place the single P-trap after the tee and run it to the wall drain.
Why not two traps? Two traps on one drain arm can self-siphon. That can pull water from a trap and let sewer gas in. A single trap with a baffle tee balances flow from both bowls. It also makes snaking and cleaning easier.
Parts you will likely need: a continuous waste kit with baffle tee, a 1-1/2 inch P-trap kit, slip-joint nuts and washers, and the Badger 5 discharge tube. If alignment is off by half an inch or so, use a short flexible discharge tube made for disposals. Avoid long corrugated sections that can catch debris.
Basic steps: 1) Hang the disposal with the mounting ring and flange. 2) Dry-fit the discharge elbow so it points toward the tee. 3) Build the continuous waste between bowls. 4) Place the single P-trap after the tee. 5) Adjust for slope and alignment. 6) Tighten slip joints hand-tight, then a quarter turn with pliers. 7) Leak-test with both bowls running. 8) Run the disposal with cold water and check again.
Tips: Keep the trap weir below the wall stub by an inch or more. Do not trap the dishwasher stub; you do not have one here. Avoid “S-traps.” Keep all slip-joint washers facing the right direction. Use plumber’s putty on the sink flange if required by the manual. If the wall drain is too high for a proper P-trap, you will need to open the wall and lower the trap arm.
Helpful visuals and manuals are linked below. They show the single-trap, baffle-tee layout. That is the cleanest, most forgiving setup for a double sink with a disposal.
External resources:
Badger 5 install manuals,
step-by-step disposal guide,
code resources, and
flex discharge tube.