I put a couple of hundred ml of acetone (all I had left in a 5 litre can) in the first water wash of my two stage, no titration, in processor water washed batch yesterday. 300 litre batch.
First wash was the acid one, 500ml of concentrated Sulphuric acid in 25litres of water.
After that drained off, the second was the acetone, mixed with 45 litres of water, washed and settled for 3hrs then drained.
The water looked very contraminated but the bio was quite light in colour.
I did a second water wash with 45 litres of water and no acetone, mixed for 20mins then left it to settle overnight.
This morning the water was crystal clear so I drained it and started spray drying the bio which was sparklingly clear in three hours.
I suspect that, as Mark found, the Acetone really helped the first water wash leaving much less contamination in the bio for the second wash to take out.