Here is my 100% Achievement guide and full walkthrough!
After the police station, we end up at Sams garage to ask a rather nervous question.
Go around the back and enter, where a bit of convo will happen..
This is another waiting for a while part unfortunately, as he messes around with the engine, feel free to look around yourself, but notice on tables to the left of Sam, there are lube bottles (engine lube mind lol)
As soon as Sam asks "How is the house coming along", Your choices of dialogue are "Physically painful" or "very slow" (something along those lines anyway lol).
After this convo, the game should autosave and this is where we can grab the can needed for this achievement.
To find it, if your standing directly infront of Sam, go to the right and behind him there is a sort of kitchen looking small area.
At the back, there is a cabinet so open it up, grab the can from the top shelf and give it to him, unlocking this achievement.
Note, you don't have to wait for him to ask you to get the can.. as soon as that autosave happens after the house convo, you can get it.
Also note, if you take too long and he cuts his hand, you will miss this and just have to replay this simple part.
Go to 50:50 to see where it is done in my video.
Hope this helps!