A much more certain way is to click on the pipe and then flush all the pipeline :
pipeline_contents.png
(Fluid pipeline sharing deliberately created here by rotating the nearby plant 4 times.)
However, it isn't obvious to new players that you can even click on the pipes themselves,
so maybe this ...

Just to add my experience, I had my EM factory set up previously & it was working and creating electrolyte. I've made many electrolyte products already. At some point, both the electrolyte and heavy oil pipes turned into holmium so it stopped working. I disconnected all of the pipes, deleted the EM ...

I just ran into this too!
Have completely rebuilt the pipes, have pumped everything out. disconnected everything and rebuilt it.
The heavy oil connection actually also got contaminated and the pipes turned into holmium. I tore it all out and rebuilt it and it stayed heavy oil.
If i leave the heavy ...