Risk of losing prime of the scavenger pump during oil change

[Dalamar]

When doing an oil change I've always just changed what's in the main oil tank and haven't drained the sump also (or what I can from the sump). I've always worried about losing the prime on the oil pump as even with just the tank oil change I sometimes get a momentary 0 psi oil pressure warning on first start. Also, previous owners had receipts that showed dealers only doing the oil tank change and charging for 5-6 L.

So, is there anything to worry about if I drain the sump oil too? I know there's meant to be still plenty of oil left in the sump for the scavenger pump to get hold of but what are people's real-world experiences? I would be a real pain if the pump lost its prime.

Is it best and safer to just change the oil in the tank more often than 12 months?

[Modrich]

I drained the sump and then disconnected the fuel pump so I could turn it over without it firing-up and top-up the oil level, i do it to half way when cold.