Servis M9409 filter

A Servis M9409 washer dryer is making “funny noises.” Evidence suggests that a tiny hearing aid battery has got past the perforations in the drum and is rattling round upstream of the drain pump.

I assume there’s a filter that stops anything dangerous getting into the pump, but how do I retreive it? The owner says there’s no easily accessible panel to get at the filter, so do I have to take the top/back/sides off and remove the hose from the drum to the pump, or what?