Usually if the soap isn't being fully washed down from the drawer it means that the water spray holes above the soap tray are blocked due to splashback....its worth taking the drawer out so you can see if they're gunged up. Fixing means that the top of the washer has to come off, followed by the top lid of the water dispensing unit now visible. Not a difficult job but there are some linkages that distribute the water to the 3 chambers which need to be carefully looked at before any dismantling commences.
John
January 2008