If you are a new nursery, you may have to cut new spools before your season. Each nursery may fashion its spools a little bit differently, but the principle is the same. It is best to use PVC that is no more than 20 inches long. A spool longer than that may be difficult to use during seeding because the seedstring will not unwind effectively as you pull the spool down the line. A spool that is too short is an inefficient use of space in your nursery system. 

When you buy PVC, it will be dirty from the manufacturing and shipping process. Additionally, during the cutting process, PVC sawdust will be created and will be stuck to your spools. Because of this, you will need to scrub and bleach your spools before winding them. Avoid letting the sawdust go down the drain by using a water bath to dip the spools in before washing. If you add slits to your spools, hold open the gap with something like a washer so all parts of the spool come in contact with the sterilizing solution.