After 5+ months of labour, I am about to take my car off the axle stands and start it up. I've had the sump cover off, so the final job is to top the engine oil up. The car is sitting level, the catch tank is filled to the maximum level per the dipstick but there is no oil in the sump. I think the oil should simply flow, under gravity into the engine? But it isn't. (I don't think it is pumped from the catch tank to the engine) The oil pump must be between the sump and the catch tank (because it scavenges the oil from the sump and returns it to the catch tank). So if there is no oil in the sump the oil pump has nothing to pump? I've done numerous oil changes prior to this and simply filled up the catch tank to the correct level, fired the car up and a little while later checked the dipstick and topped up if necessary. I may be overthinking this and what I really need is a lesson in basic dry sump engines.