There is no mention of a filter in the manual.
The detergent dispenser should be taken out and washed clean regularly, have you done this?
If the drain duct gets clogged then that can cause inadequate draining. The drain duct is where your outlet hose fits into, and should be between 65 and 100cm from the floor.
If you haven't got your manual see here:
http://laundry.manualsonline.com/manuals/mfg/ariston/a1636.html?idRes=600341
ChicksFan, April 2012