Re pipe.
Not sure if you intend to put it in the ground or not but a very tough pipe would be MDPE eg like this
https://www.toolstation.com/mdpe-pipe/p11290 or larger Dia.
I think B4RN use something similar and the fittings.
Best way to get a string through it, if you have a Air compressor.
1..Get a small piece of foam rubber, or piece of cloth,
2..tie a knot around it on some 'string', push it in the end of the pipe but make sure it's not to tight a fit,
3..then blow air into the pipe and wait for the string to come out the other end.
Once the string is through tie a thicker rope to it and pull that through.
Then tape (I use insulation tape) the end of your cable to Plus any extra 'Draw Rope' to your draw rope, then have someone pulling at one end of the pipe and have another person feeding the cable and extra draw rope in.
Another way is to push the cable into the pipe before it's installed and maybe tape some string to it and pull that in at the same time.
In a past life we used to feed a steel draw wire in to Conduit then attach up to 25 cables to it and 'Winch' the cables in and your fingers if you did not keep them out of the way.
45 years later those circuits are still working