Just finished re-piping the kitchen sink and learned a ton about traps

I dealt with something similar when we moved into our 1950s ranch. The previous owners had done a "handyman special" under the kitchen sink, bypassing the old drum trap with a straight pipe that went right into the slab. Every time the sink drained, you could smell that distinct sewer scent. It's crazy how often people think a straight shot is better for flow without realizing they're just inviting gas back into the kitchen.

When I swapped out my old unit for an InSinkErator Evolution, I realized the dishwasher tailpiece was also sitting too high. I had to drop the wall connection by about two inches to get the P-trap to sit right and still have enough pitch. I used a Fernco coupling to transition from the old galvanized pipe to the new PVC, which made getting everything level a lot easier than trying to thread into the old iron.

It really is a relief once you get those slip nuts tightened down and see no leaks after a full cycle. That Badger 500-1 is a workhorse, but it'll definitely vibrate things loose if you didn't get those O-rings and seals perfectly seated. Glad you caught it now before that sewer smell really started to permeate the cabinets.

My struggle wasn't just the trap itself, but the height of the wall drain stub-out. When I replaced my old cast iron with a deeper Kraus sink, the drain exit in the wall ended up being too high for a standard P-trap setup to drain properly by gravity. I had to open the drywall and lower the sanitary tee by about four inches just to get enugh pitch so water wouldn't sit in the bottom of the sink. While you were fixing that seal, did you check the dishwasher's high loop? Even with a solid trap, I found out the hard way that without arching that 5/8-inch hose up against the underside of the counter, I was getting backflow from the disposal into the dishwasher. It’s those hidden details behind the InSinkErator that usually trip me up more than the actual PVC assembly.

Since you were alredy rearranging the under-sink geometry to accomodate the new P-trap, I hope you took the opportunity to verify that your dishwasher drain hose is correctly configured with a high loop fastened to the underside of the countertop. Without that specific elevation change or a dedicated air gap, you run the risk of gravity-induced backflow where dirty sink water or even macerated food waste from that Badger 500-1 coud potentially migrate back into the dishwasher tub. It is one of those technical nuances that often gets neglected during a hurried retrofit, yet it is absolutely vital for maintaining proper sanitary conditions within the appliance's internal hydraulic circuit.

Those old grease boxes were a real headache. Used to see 'em buried in the slab, ussually half-rotted out and smelling like a dead animal. Glad you got rid of it. Back in my early years, we’d have to lead and oakum those cast iron joints to get a seal, but these plastic kits make it easy to miss the pitch. Just make sure you didn't leave a 'belly' in that horizontal run. I’ve seen folks swap a grease box for a P-trap and end up with a standing pool of gunk becuase the wall pipe was back-pitched for the old tank.