Disposable Diapers are NOT washable!

We are potty training our 2 year old son. He has had a habit lately of taking his diaper off and going potty himself. Great.... right? Well here's the thing.... The diaper ALWAYS comes up missing. We can never find where he disposed of it at. His place to "throw it away" had been "sissy's trash." We use cloth on our 6 month old and have a kitchen trash can in our laundry room for her diapers. He would just open the lid and throw it in there and then run into the bathroom and go like a big boy. We thought we had solved that problem. We made sure the bathroom trash is always empty so that he can dispose of it in there. He's been doing so well..... or so we thought. I did a load of diapers tonight and as I was pulling the wetbags and the covers out, I found a disposable diaper that had been washed. Given it is now just the outer shell of this diaper. I'm kind of scared as to where the rest went. Guess I need to pay more attention to what he's doing with the diaper he's taking off.