The official advice is that all items being recycled should be clean and dry. My dad (a retired engineer) always poo-poohs this as he reckons the heat of the recycling process is enough to burn off any food or toiletry residues in the bottles.
Do you always ensure your bottles are clean and dry before recycling them?
No, I heard (like your Dad) that the recycling plants can clean them out better and than we can so it's a waste of water and energy. Don't know if that's true, but we don't have a dishwasher hand washing all the tins and bottles we recycle would certainly be pretty inconvenient.
I try to wash and dry all my recycling items but occasionally it's just not possible - some bottles have tops that I can't remove or shampoo bottles never seem to come out clean.... and at those times I just hope that my dad is right. I do think that perhaps the water I use washing them might out weigh any benefit from the recycling.
We do not re cycle in our Shire -they say they do it themselves but have seen a programme saying they do not!
However even when I was sorting in the country, I would not wash bottles -what a waste of water -we have water restrictions here every year as dams are so empty and I would consider this an awful waste of water.