Last year I had to clean my plastic bong and I remembered
reading that acetone was great at washing glass. I was unsure
if plastic would handle it so I googled it and found a site
stating that plastic and acetone mixed well. After actually
doing it I found that alot of the plastic inside had "melted"
and twisted - there was plastic "spaghetti" in the bong and
it generally looked like someone had filled it with gross
snot. The bong still worked though, but I retired it just to
be safe. Lesson learned: Don't wash plastic bongs with acetone.
It works well on my new glass bong though.