The thing is, yes a pump might be to much pressure, but loosing it back into the inlet, via a valve, seems to take almost all the pressure off the filters.
Putting Waste engine oil through a simple bed sheet filter should remove any bigger bits of muck, certainly enough for it not to be harmful to a 105, I would have thought.
I guess a gear pump may be designed to suck, but I suspect that a 105 would struggle to suck through a filter. I've just realised that have implied almost the exact opposite on a thread on the VOD. I'd better shut up.