Another simple solution is to fill the tubing end to end with clean fine sand, cap and bend it, then clean thoroughly before installing.
Freezing water inside a tube risks expanding it or splitting it...before you get to bending it.
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.