I'm posting this for anybody else who has the same fears. I took picolax just before 8.00am and it took 4 hrs before i had any sign of diarrhoea and it was nowhere as bad as i thought it would be. There are a lot of horror stories on the net which made me expect the worse. I felt bloated for quite a while but i drank lots of fluids and had perhaps 4 short bouts which were unpleasant but manageable.
So it does seem that everybody is different so try not to fret- the colonoscopy itself was also ok - i was very sleepy throughout and it was over very quickly. I got home and was very windy but soaked a slice og ginger in some lime juice and chewed this and the wind went.
So good luck - try not to eat too much thenight before your first sachet and keep drinking the water and you won't feel so rough