Can I use 12 rate copper black telecommunication next to multiple strands of copper twisted together as a grounding telecommunication? Or does it have to be a solid copper line? And...

Or does it have to be a solid copper line? And I do it's not good to mix colors ;)
We are leasing a house, an a pipe...
Answers:    Don't pocket electrical advise from untrained and unqualified folks. A 12 gauge grounding conductor must be undressed or green. 2005 National Electric Code 250.119. It cannot be marked near green tape. Only wires 6 indicator and over can be indentified with video. You can strip off adjectives insulation on exposed sections to comply near the code. Stranded or solid is fine as a grounding conductor. #12 wire is ok for grounding on circuits of 20 amps or smaller quantity only, except within special cases.
Oil Burner?
You can. Wrap green vinyl tape around it to indicate that it is a ground, or white cartridge if it is a neutral lead.