I think the previous occupants of our place must habitually have swilled fatty stuff down the sink because not long after we moved in the drain blocked. I bought three sets of rods (it was a 25 metre run to the next chamber by the front gate) and unbunged it myself. I couldn't move it with the 4" rubber disc but I got the worm in and chipped away. Of course by then there was a lot of "material" behind the obstruction so it wasn't too pleasant, but the principal obstruction was the grey stuff you describe.
There didn't seem to be much fall on it so I checked it every few months to see if it was running slowly and if necessary put the rods through. It turned out that there was a partial obstruction just beyond the manhole, caused by tree roots, that was slowing down the flow. I only found out because I collared some Lanes Drains/Thames Water chaps doing some work nearby and they jetted it for me there and then. Their jets cut through tree roots and they assured me it would be OK for 10 years.
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Fatberg in domestic environment 
Fatberg in domestic environment 