Oil sensor port is a good location: it's downstream of the engine's oil pump and the engine's oil pump will act as a check valve (with a small leak). Pump the oil into the sensor port and the engine's top end gets lubed, too. One of those el-cheapo water pumps that you stick in a drill works OK with the 15W-40 oils. As whunter says: get the new oil to run out of the drain plug and you're done. Up here, with the winter stored farm tractors and trucks, we then stop, put the pan plug in, fill with fresh oil, cold crank for a couple seconds to make sure the pistons are free (oil has been put in the glow plug holes in the fall), then glow and start.

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daBenz - 1970 220D