What must be ensured in the fill pipe installation to avoid liquid collection?

To avoid liquid collection in the fill pipe installation, it is essential that the pipe is installed without sags or traps. This is because any dips or low points in the pipe can create areas where liquid can accumulate instead of draining properly. When liquid collects in these sags or traps, it can lead to issues such as overflow, contamination, and it may even block the flow of future fills. Ensuring a smooth and uninterrupted slope in the fill pipe allows for proper drainage and minimizes the risk of liquid retention, which is critical for maintaining system efficiency and safety.

The other choices relate to different aspects of pipe installation but do not address the specific issue of preventing liquid collection. A straight pipe is beneficial for flow but does not guarantee that there are no low points. Insulation may be necessary for temperature control but does not impact collection directly. Thickness of the wall can relate to strength and durability, but again it is not a factor in preventing liquid from accumulating in the pipe. Thus, avoiding sags or traps specifically addresses the concern of liquid buildup in the fill pipe.