I am your bulk motor oil delivery guy and I have a question

Hey y’all I deliver er bulk motor oil to shops, mechanics, and fleet service places.

We do everything from 0-16 to 15-40, motul, cam2, chevron, petro Canada.

We are supposed to do line changers between different tanks. So if I’m doing 5-30 syn blend and going to do 5-20 full synthetic next, I am supposed to stop filling the tank 15 gallons before it’s full, swap products than start filling again so I can push 15 gallons of the 5-30 syn blend out of the line.

I hope that made sense.

I am not a car guy so I don’t really know the difference in the oils or much other than 10-30, 15-40 are heavy and others are light motor oil.

What happens if I don’t do my line change? I can’t imagine 15 gallons of different light weight motor oil in 250 gallons of something close would hurt anything would it?