Whenever we think about modeling pipes the natural tendency is to look for an appropriately sized piece of tubing, usually plastic of metal of some sort.
A cheap and often much stronger alternative is to use wooden dowel. This can be purchased in a regular DIY store in a variety of sizes and at a variety of lengths. One of the main advantages of dowel though is its strength when compared to plastic or metal pipe of a similar diameter.
You may need to give the dowel a quick sanding to get rid of any rough edges but once it’s painted it can be hard to tell apart from more conventional tubing.