This is not specifically an appliance tool, but I have used it for that purpose occasionally. If you have not seen the usb endoscope cameras coming out of China and for sale on all popular on-line marketplaces, you need to have a look. These use a laptop for power and display with a simple usb connection. They have either 4 or 6 LED's for lighting in the camera head and use a 1/6" CMOS camera mounted on a tiny circuit board and housed in an aluminum tube with lens....all waterproof(as advertised, anyway). I purchased a 10 meter unit for about $20 a year ago just to tinker with it. Was surprised at the clarity of the images and the depth of field in daylight.
I've modified mine for use in plumbing applications by carefully separating the USB plug housing, desoldering the conductors from the board, running the cable inside a 25' metal spring-type sewer snake, then resoldering the wiring and reassembling the plug case. I also built a protective housing from a drilled 1/2" PVC cap with female threads and the bottom part of a 1/2" threaded sprinkler riser. This keeps the camera up off of the bottom of the pipe for better images, and enabled me to add more waterproofing around the camera and lens. The snake allows me to push the camera into plumbing drains and wall spaces. I thought it would last a day or two, but have used it on many occasions in the past year and it's still going strong. For $37 and a few hours brainstorming, it's been well worth the effort. The most worthwhile use for me has been locating plumbing drain breaks under slab foundations.
Here's a pic of the business end: