We keep ours outside
We had a odour trap bin and literally never used it!! Sound that it's just as easy to put the nappy bags outside the back door or straight into the black bin. Even when upstairs I just chuck the nappy bags out the window into the garden and they land by the back door with the others. The refills for the odour bins are so expensive and just not worth it!
We literally just have a little pedal bin next to the changing table in the nursery. We take it out every day so it doesn't smell.