It's hard to find a competent plumber. The one I hired to add a sediment filter to our well water supply did not do such a swift job, or he used an inferior part. Either way, I'm left with a mess as water continually leaks from the filter's pressure relief. Luckily, there is a drain nearby, but the mess on the floor was intolerable. So, I put a plastic container underneath to catch the drips. It needs to be emptied every day (2 at the most) or you get an even bigger mess trying to empty it. So, how about a passive siphon that "activates" when the level rises sufficiently?
The parts I used can be found in aquarium shops and in your local hardware store.
Nylon tubing (1/4"OD by 1/8" ID) - Length determined by distances in your situation
1/4" drill bit
32 oz. plastic container (to fit easily under the filter)
Silicon aquarium sealer
Medical Tape (just want something sticky and not affected by incidental moisture contact)
Sandpaper (60 grit)
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Step 1: Preparing the Container
The container must have a hole of the proper diameter to accommodate the tubing. This size tubing is what I had on hand, and it works fine. Too large a tube, and you may not get the siphoning action you need. Too small and there may be insufficient pressure to allow the siphon to work efficiently enough to empty the container before it overflows.
I used the quarter inch drill to hand-bore the hole a few inches from the top. This is important; if you simply run the tubing over the upper edge, there will be insufficient pressure to start the siphon action. By having the capability of a couple of inches of water over the tubing, you guarantee enough "head pressure" to start the flow.
Use heavy grit sandpaper to rough up the outside of the container, both inside and outside at the hole, and near the bottom of the container where the hose will be attached. The plastic container I used was exceptionally smooth and required this. A different adhesive or different attachment technique will change what you do.
Step 2: Running the Tubing
Once the container is prepped, you can place the tubing through the hole. Allow at least 1/2" (12-15 mm) between the end of the tubing and the bottom of the container. There will be some movement in the tubing during the adhesive process and junk might be sucked into the tubing during the siphoning if it's too close to the bottom..
Glop some aquarium sealer near the end of the tubing and hold it in place (I used a woodworking clamp) for 24 hours to allow the adhesive to set.
Once that was done, glop more adhesive at the hole, both inside and out to completely seal the container to the tubing. Again, 24 hours is required to cure the sealant.
Once the adhesive has completely cured, and to insure the siphoning action, tape is used to hold the tubing to the side of the container.
Step 3: Testing and Installation
I tested it at my kitchen sink first first to make sure that (a) the device would work, and (b) that the seal was intact. I very slowly poured water into the container as it sat next to the sink. When the level reached about to the top of the tubing, the siphon action began. It took 20 minutes to empty 30 oz (450 ml) of water from the container. The lower the exit end of the tubing, the faster it will drain. In any case, the size of the tubing will be the ultimate determination on the efficiency of the drain and establishes the limits of the leak it can handle. For my purposes, 20 minutes is more than fast enough.
I took the container to the basement and stuck it under my leaking filter. I ran the tubing down into the floor drain, refilled the container (but not completely) and waited.
I was rewarded when I returned several hours later. The container was emptied, and I did not have to lift an additional finger to get it that way!
Step 4: Potential Improvements
The tubing is a bit awkward to work with and doesn't like to be bent to sharply (closes down). It might be possible to apply a bit of heat to the tubing to make it bend and hold shape. That said, if the internal bore becomes more restricted, the water will flow slower. Always a tradeoff!
Another alternative would be a flex straw to exit the container. The attachment of the tubing becomes problematic, but this could be used.
The most elegant way would be to use a "U" type of aquarium connector through the container wall with the tubing then attaching to the "U" fixture more easily. Only one sealing/bonding step would be performed, saving time in construction.
UPDATE: I discovered a "vapor lock" problem. Specifically, if, near the point at which the tubing turns downward, there is an air bubble, then it takes much more water in the container to start the siphoning action. I did not see this the first time it siphoned because the tube was empty. I had re-arranged the container and tubing, and introduced an air bubble. The airbubble will compress, and the capillary action of the tubing will provide back pressure to the bubble. I am waiting for it to re-fill (the tubing now is full of water, no air) to see if it will continue siphoning. If it does not, bye-bye instructions!
04 March 2014: Success! The siphon works flawlessly. In fact, so much so that I had forgotten to check on it for the last couple of weeks because it never overflows, but keeps draining as it should! No air bubbles in the tubing, and it works great!