I had to do the same fix recently after leaning on and breaking the plastic tube on a weekend with no options other than a length of copper heating pipe .
I later read up on possible issues with copper leaching into coolant thus contacting the alloy of the engine .
I can`t remember all the details but was convinced to buy an 8mm internal diameter rubber coolant hose and 2 alloy connecting sleeve tubes .
I noticed the copper has turned blue where it contacted coolant . The motor has only run a couple of hundred miles with the copper pipe .