We use these all the time. They take a lot of practice to become really good with one without making a big mess. A 36" bit (IMHO) would be useless. The extensions are stiff, so the flexibility would be lost. We use the 72" models.
Tip for use:
1. Use a power drill, not a cordless
2. Use the placement tool.
3. When drill across floor joist, drill your first hole with at least a 1" spade bit. Make that hole about 1 1/4" from the bottom of the joist. The hole helps you to guide the bit with the placement tool through the other joist. Be carefull to get it started straight and low or you'll be repairing the floor above.
4. IMPORTANT!!!! As the bit goes through the wood, Stop the drill quickly and push the bit to the next joist/stud. This way you can feel the bit hit the PVC waste line before you drill it.
5. Always keep 2 of these bits on the truck. They will break where the drill meets the shank and you'll hate it if you can't finish because you break one.
6. Purchase the model with the auger and screw tip. When the leading edge of the auger get dull, the bit will not go through.
