I recently changed oils using the pump method through the dipstick hole. Of course I do not know hoe much more oil was left in the pan, how deep the cable went.

For my next oil change I will surely use the sump plug. It is a 13mm size and I could not undo it using a normal 13mm spanner. I then tried a big adjustable spanner but that was about to round the edges off so I stopped immediately. I then used a 13mm socket and a ratchet and that did it.

The washer is not copper but leather/felt material. For a 13mm bolt it surely put up a lot of resistance.

By the wey if I remember correctly the bolt was hexagonal but the socket was not - that is not a good idea since there is the possibility of the socket rounding off the edges. For such bolts you need a hexagonal socket that is a 100% fit.