I have just installed my third insinkerator (Model 43). In the same sink. The first one lasted 15 years. The second one only a little over two years, just exceeding the manufacturer warranty period. Having opened up the second failed unit, the following is a short cautionary tale.
For those who do not know what an insinkerator is, it is a widely distributed brand of in-sink waste disposal unit, actually designed in Wisconsin, USA. It is the most common brand sold in New Zealand and Australia.
The unit failed to grind one day. The motor just hummed but the overload cutout did not operate. Suspecting a jam, I turned it off and used the supplied Allen key to turn the grinder by hand from underneath. It was surprisingly easy to turn, so we did not have a jam. When I turned it on again, same effect, just a hum but the grinding plate did not turn. I extracted the food scraps manually - a lot of fun; ensured the plate was free to rotate then tried again, but achieved the same lack of success. I could see no other way forward than to replace the unit.
This took me a few hours, mainly due to the fact that the locking collars holding the unit under the sink had rusted solid. A lot of WD-40 and tapping and levering later, it came out. The two following photos tell the story. I did take the unit apart to try and determine the problem, knowing that the warranty had expired.
The first photo is the interior of the grinding chamber. Look at how it has rusted. This has nothing to do with the fault, neither is it faulty installation practice. This is what will happen inside all of them. The parts are not stainless steel. The second photo shows the grinding chamber housing plus the collar and clamp that hold it to the sink. Clearly water had been leaking from the sink under the flange although I had not been aware of any water pooling under the unit.
I actually plugged the unit in while dissassembled as in photo 1. Again just the hum but no words. None the wiser as to why it had failed, I then removed the motor housing and guess what? Rust inside the motor, inside what is meant to be a completely sealed section.
I didnt try and analyse this further; once water gets inside a motor all bets are off. I do think this is a manufacturing fault, since no amount of water, either from the grinding chamber, or by leaking down from above should be able to get inside the motor housing and if it does, then the design of the water seals or assembly of the product is inadequate.
On installing the replacement unit, I ensured the seals at the sink flange were coated lightly with a sealant and ensured they were all seated properly. Once the insinkerator was tightened up against the mount plate, I used a short piece of steel wire to tie one ear of the locking collar to the mount in order to stop it rotating loose. The design of the friction locking arrangement is not that good because there is not much to stop it vibrating loose over time and these insinkerators vibrate madly when grinding things like fruit pips and other solid food waste. Finally I coated the steel locking collars and fittings with WD-40 so that if water does leak down they will not rust up quite so easily. I will also periodically check for drips. Thats all that can be done.
So, why did I buy another of the same type? Well, Bunnings did have some other brands; some were cheaper, others more expensive. I didn't want to pay any more money and I had not even heard of the brands that were cheaper, so I took the approach of the better the devil you know.
These waste disposal units are easy enough for a reasonably handy DIYer to replace. The trickiest part is holding up the unit from below while trying to lock off the clamp with your other hand. Two people will be helpful for this part. The only other part is reconnecting the waste drain couplings, which is no real problem if they are in good condition. You might want to inspect the waste pipe section for the condition of its internal mating seals and also to clean it thoroughly. Installing a new insinkerator from scratch would be a bit more work. You would have to make the appropriate sized hole in the sink and also create a waste junction point and mate this up to the insinkerator. These jobs are better left to a plumber, who has a collection of fittings in his truck.