Hello, probably I didn't understand the essence of your problem, but there is a way to turn all your digital oil without having to deal with any byproducts.
There are 3 templates that allow you to work with oil products and they replicate the full cycle of vanilla advanced oil processing. Here is a breakdown:
"Chemical Template: Advanced Oil Processing" - it consumes digital crude oil and digital water and turns it into 3 products: digital heavy oil, digital light oil and digital petroleum gas. It happens when you have digital petroleum gas as a filter in a cell
"Chemical Template: Heavy Oil Cracking" - it consumes digital water and digital heavy oil to produce digital light oil. This happens when you have digital light oil as filter in your chest
"Chemical Template: Light Oil Cracking" - takes digital water and digital light oil to produce digital petroleum gas
That means that if you meet following conditions (bellow) you would turn all your digital crude oil into digital petroleum gas
1) You want to have all 3 chemical templates in a chest
2) You want to have a filter set for 2 products: Digital Petroleum Gas (to trigger both Advanced Oil Processing and Light Oil Cracking) and Digital Light Oil (to trigger Heavy Oil Cracking)
Also, templates are processed in a specific order, line by line from left to right, so try to put Advanced Oil Processing template as a last one, so it will try to create Petroleum Gas from Light Oil first. Same goes to other templates, try to prioritize them by moving their positions in the chest