Hello,
If you are getting good water flow through this section on the final rinse then it can only be a blockage in the tray itself.If you take out the drawer by depressing the button in the centre of the drawer.then wash all the old detergent under the tap.Then remove the small insert in the fabric tray you will see normally 3 raised tubes,these need to be clear and also the part that sits over them,you should clean it thoroughly then refit and try again.

Hope this helps.