Measure the amount of electrical wiring you will have to waterproof with a tape measure and write this number down. Also count any electrical joints or connections and make a note of that as well.
Purchase silicone sealant and enough heat-shrink tubing to cover any electrical joints you will have to waterproof.
Mix silicone sealant, if needed, according to the instructions on the package. Use a small paint brush to apply a thin layer over all the wire you will have to cover. Allow adequate drying time according to directions on the silicone sealant packaging.
Fit the heat-shrink tubing over all electrical joints.
Plug in the heat gun and melt all the heat-shrink tubing over the joints. Allow time for all the joints to dry completely.
Run your wiring through the PVC pipe for your project.