|It's not a good idea to use a real pure soap product on diapers. The soap can cause a waxy film (like soap scum on your shower wall) and reduce absorbency (or even cause repelling outright, this would be more likely with pocket diapers but over time you never know...). I've also heard that Fels Naptha in particular is quite a harsh soap but I don't know much about what consequence it would have for diapers or fabric in general.
Honestly though, if you're only dealing with exclusively breastfed baby poop, then you don't need to remove ANY of it before putting them in the pail. As long as you run them through a pre-rinse before the full hot wash then you'll be fine. Breastfed baby poop is water-soluble (so it'll rinse out easily in the pre-rinse) and it hardly smells (so won't cause horribly nasty odors in your pail). There's no harm in rinsing it if that's what you prefer, but it's really not necessary at this point. I say take advantage of it while you can because once your little on is on solids or formula then it's a whole other ballgame!!
For when you are dealing with solids or formula poop (or if you prefer with breastfed poop) I would recomend a diaper sprayer. It's a bit of an investment (anywhere between $35-$50 if you buy it, or slightly less if you make it yourself using parts from the hardware store like a kitchen sink sprayer) but totally worth every penny in my opinion... Although even at that point lots of people will just shake the diaper over the toilet, what falls in gets flushed and they let the washing machine deal with the rest. Many do really rinse the diapers fully, removing every trace of poop and that's fine, but just so you know it's more a matter of personal preference rather than necessity.