I had a situation where I needed to replace an underwater light in a pond. The problem was that somehow (bad glue joint?) due to a leak, the conduit from the light niche to the j-box above water level had attracted tree roots and the conduit had gotten plugged making it difficult to remove the old light cord then pull in a new one.
So I made a mini-rooter out of: (list of materials coming up...)
* Safety glasses and snug fitting gloves (you don't want them getting wrapped up in the spinning tape)
* piece of electrician's flat steel fish tape (I had one I'd found at a job site with the handle gone and the tape sprung out) (Incidentally, this material is useful for many purposes being tough but flexible. It will take a sharp edge and hold it for a while as long as you don't overheat it while sharpening)
* drill (in this case a cordless one...not crazy about standing in a pond with water up to my knees and having a live tool in my hands.)
* piece of flexible electrical conduit as a guide for the fish tape
* pair of pliers
This process should work in any small diameter pipe. Just be aware that metal WILL cut plastic and you don't want to compromise your piping any more than it already may be.
Step 1: Cutting Edge Technology
1. Determine how long the rooter needs to be (by feeding it in and finding out where the obstruction starts if you can) and roll that much material off the fish tape roll. add another 3-4 feet or so to work in and bend the tape sharply with a pair of pliers. It will break rather than bend all the way over. If it does bend over, unbend and work it until it breaks.
2. Sharpen one end carefully on both sides and the end. You do both sides so that you can reverse direction and still cut.
3. Carefully make a slight bend at the end. Not too much otherwise it may be hard to negotiate bends etc.
4. Feed the tape into the conduit or pipe as far as it will go, then slip the flexible conduit over the exposed section then chuck it up in the drill. The conduit itself will act as a guide for the section already in, and the flexible will support what you will be feeding in.
5. Very slowly start the drill (in either direction and make sure that the tape is actually spinning. If you need to back it out a little before the obstruction and get it going first, do so, then slowly advance it while it is turning.
6. When you have fed it in as far as the flexible conduit will allow, if you want to go further, you can either use a shorter piece of conduit for a support or try and just carefully (with gloves!) hold the tape loosely and feed it in some more.
7. Reverse the drill and spin it slowly while backing it out.
**A note of caution: the tape may be twisting along its length without actually spinning and if you go too far without it actually spinning, you could snap it off in the conduit then you'd be double screwed....
Step 2: Check for Success
If you are successful in clearing the obstruction, you should be able to use another electrician's tape or a shop vac to suck a string through for pulling the new light cord.
In this case, I used a second fish tape from the niche, all the way to the junction box and pulled a rope back to use for the new light cord.
Step 3: Done!
A word of explanation for those who wonder about this "new light cord" stuff. Underwater lights typically come as a sealed, water-tight complete fixture with the cord already attached and you order it with the intended cord length (usually in increments of 25'; so you might have a 25', 50', 75' cord etc. and you cut off the excess at the junction box above water level when you splice it into power). There is typically enough cord coiled up behind the fixture in the niche to take the unit out of the water to remove the lens to change bulbs but sometimes the fixture itself leaks and that is something that is not easily remedied so the only good solution is to pull out the old light and pull in a new one.
In this case, I attached the rope to the end of the new light cord and pulled it back up to the junction box. I cut the cord to length and spliced it into the feed, put the cover back on the j-box and cleaned up.