Most busbar bending machine including AEG and Ariston will have their waste pipes plumbed to the sink U bend or into a plumbing out kit, that’s the small kit that screws onto a U bend or a part of the waste drain pipe and cuts its own hole into the pipe as you tighten it and the appliance outlet pipe connects onto the plumbing out kit.
Connecting your washing machine drainage outlet pipe to the U bend under a sink can cause back flow of dirty water into your appliance and this can cause both flooding and a foul smell to build up in your washer, also it could mean that part of the water in your wash could be dirty, the dirty back flow water from your sink can also cause the interlock to lock the door, this could happen even if there is no electrical supply to the machine, the locking system can often detect even small amounts of water.
Connecting your washer drainage pipes to a plumbing out kit or to a U bend under a sink can also cause blockages at the point where the washing machine drain pipe meets the plumbing out kit connector or the U bend connector as both connectors push into the washer drain pipe and both are slightly smaller than the pipe causing a bottle neck affect that can lead to blockages, this will also cause the machine to report a error and keep the door locked with your clothes trapped inside, to clear this problem simply take the washer drain pipe off the U bend/plumbing out kit connector and hold the pipe into a bucket and put your washer on to a drain/short spin cycle, the washer should empty its water and door should open after its predetermined delay time, then you can clear the blockage in the pipes and reconnect the appliance to the connector
The best way to plumb most appliance waste drainage pipes including AEG and Ariston washing machines is into a free standing 40mm waste pipe if you are in the UK, the pipe should be about 3 to 4ft high and the washing machine pipe should be put in the top of the pipe to a depth of about 6 inches, this is not the most popular method but it is probably the best method that will give the least amount of long term problems and it is also the method most washing machine manufacturers recommend you use.