PVC pipe is the white stuff that's sold for "potable water" and is used in supply lines to bring water to your tap. It is a little more "brittle" than ABS, but is pretty strong. It is available in a range of "thicknesses" but "Schedule 40" I believe is the most common and should be sufficient.

If you intend to glue a cap on one end, you will get best results using the PVC Pipe Dope sold at the lumber yard or hardware store. If you want a "pressure tight waterproof joint" the use of the "Purple Primer" sold at the same places is recommended (but be aware that it stains everything it gets on - PERMANENTLY). For a shipping can you should be able to omit the primer.

ABS pipe is the black stuff used for sewer and waste lines. It is a little more flexible than PVC, but overall strength isn't significantly different. One reason that ABS is not used for "potable water" is that it often outgasses residual chemicals for fairly long times after manufacture. For many uses this isn't objectionable, but the "delicacy" of your bow hairs might make one suspicious of its suitability here. There is a separate ABS Cement at the lumber yard for gluing a cap on the black stuff (and which quite incidentally is an excellent "glue" for lots of ABS body parts on recent model automobiles).

With either type of pipe, once one end is stoppered with a glued on cap, the slip on cap that you push in place on the other end can seem to have become "permanently attached" and a good grip and agressive torque may be required to get one off after it's been on for a while. (On pipes I use for tool and part storage, I usually drill a small hole in the cap on the loose end. A blast from the "sweeper nozzle" on your handy shop air compressor, aimed in the general direction of the hole, usually will lift the cap right off.

Fittings to provide a threaded end so that a screw on (or screw in) cap/plug can be used are available, but add some bulk to the can.

John