I'm trying out this mod for the first time and I'm kind of stuck at science pack 2. I've researched everything that only needs science pack 1. Now I started producing science pack 2 for further research but it produces some purple fluid which I can't use for anything and I can't build reservoirs because I can't research them yet.

What am I missing?

In the next research, Science pack 2 will be released.
Automation -> Electronics -> Automation 2

However, it is not guaranteed when applying this mod from the middle.

I don't understand what you're saying. I have automation 2 already. I can make science pack 2 but it produces purple liquid I can't get rid off so I can only produce 4 science pack 2

Finally got a name for the purple liquid, it's sewage. no idea how to get rid of it except placing and removing the assembly building

Purple liquid is sewage.
Because there is little utility value, It should be poured into a steam engine and discarded.
Otherwise, the assembling machine is clogged.
This is a specification. Please also refer to the following article.

https://mods.factorio.com/mods/die_8_/hard_vanilla/discussion/5118