Sink water gushing back into washing machine

[borlorjee]

My washing machine's waste pipe doesn't seem to be long enough. It sort of droops downwards when attached to the sink and the sink water returns back into the washing machine now and then. Is there any way to fix this? Would a extension pipe fix the issue? Also, is it normal for this to happen when the pipe is placed downwards rather than upwards? 

 

Thanks!