Not sure I can help with the garlic issue - though I grew-up with garlic in EVERYTHING, I barely cook with it because I taste it for days afterwards.
The poop, though......
We had 2 kids in diapers last summer - a 1 year old and a 3 year old who both have excellent digestive systems. We keep a trashcan upstairs in our laundry room and in the garage for stinky diapers and make sure both always have a liner in them to prevent the odor from permeating into the plastic.
We purchased some of the refresheners that absorb the odor from the environment (they have a gel-type substance inside a plastic tub that you open and leave in the room for a month). We got them at Lowes, and they seemed to help. We also use both Glad and Febreeze plug ins, but they seem to run out quickly. We purchase the refills at Sams Club and Costco to help reduce the costs.
My only other advice would be to put in a ceiling fan or put a fan in an unreachable place in the basement to help keep the air circulating when you can't have the doors open to help dissipate the scent.
Good luck!