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Slugs for Solving Bio-Film Problems in Floats, Tanks and Pipes

Oregon is a funny place. We recently changed our State bird from the Meadow Lark to the Osprey, mostly because several other States were claiming the Meadow Lark, and Oregon likes being….unique. Some would say bizarre. Our State Flower is called Oregon Grape, and of course, is not a grape at all. But it is in the business of State Mollusk that we really shine. We choose…The Giant Banana Slug.*

Average size Giant banana slug with a normal size banana


Everyone in these parts has Slug stories. Slugs in the kitchen, slugs in your toilet, slugs in your carburetor. Slugs are simply part of life here. My favorite story is the day I forcefully slid my foot into a Muck boot, only to find the toe filled with a now-pulverized puddle of slug guts. It was horrible. In the end, I tossed my sock into the woodstove and threw the aggrieved boot into the front yard for the rest of the winter.

How About a Happy Slug Story?

I recently had the opportunity to spend a few hours wandering around a grazing operation, looking at grass and cattle and fencing and water systems. This is about my favorite thing in the world to do: spending time with fascinating people who are looking for answers. On this day, we looked at several water tanks, tanks equipped with various kinds of automatic floats that controlled the level of water in the tank. The landowner talked about the pros and cons of each style of float, but noted that all floats suffer from problems associated with water quality. Specifically, float valves tend to suffer from what is called “bio-film”, a slimy, slug-like film that sometimes grows inside the float and eventually causes floats to fail. This is especially a problem in systems using natural surface waters that include high levels of nutrients. Bio-film is a community of billions of tiny organisms, bugs that are busy eating and reproducing, converting nutrients into ever-more gooey film/ slime that gums up pipes, hoses and floats.

In another life, I worked on community drinking water systems, some of which were plagued by these same bio-film problems. And while there are different ways of dealing with bio-film, my favorite technique is known as The Slug Method. It’s simple and inexpensive, and if you have problems with slimy gunk inside of your floats or horrible organic smells coming from your faucets, you might give this a try.

The Science

The bio-film problem is biological: these are live “bugs”. The issue is finding a way to kill them. The weapon of choice in this battle is the chemical chlorine, chlorine in the form of liquid bleach, the same stuff you use to disinfect and brighten your laundry. Chlorine is very effective at “oxidizing” organic material, and it makes no difference whether the material is dead or alive: chlorine molecules will “burn” it. Bio-film can easily be burned away and killed using household bleach. The difficulty is in getting the chlorine molecules to the place where they can do their work. [Note: I do not recommend dumping chlorine down your well as a way of combating bio-film.]

The Slug Method

The slug method uses a small dose of relatively strong chlorine solution to burn bio-film. A small volume of chlorine solution is introduced into the system at points like faucets or union fittings in the pipeline. This “slug” of chlorine is then allowed to travel slowly downstream from the injection point, killing nearly every living organism it encounters, eventually ending up in your water tank, where the killing continues. Bacteria, bio-film, algae, virus: all burned to death by bleach.

Steps for Killing Bio-Film With the Slug Method

1. Go to your laundry room and find a gallon jug of bleach, one that is nearly empty. If it has an inch or two of bleach in it, that’s about perfect. Fill the jug with regular tap water. You now have a gallon of 1% (or so) chlorine solution. This is enough chlorine to kill about a bazillion bugs.

2. In the field, de-pressurize the hose that leads to the float and tank you want to disinfect. Disconnect from the hydrant, drain the hose and empty the tank.

3. Using a household funnel, pour the contents of the bleach jug into the hose or pipeline. Although you have already diluted the bleach to around 1% chlorine, I always suggest using disposable gloves and safety glasses.

4. Set the faucet at a very slow drip. (If you are using a frost free faucet, add a small, threaded ball valve to the faucet, open the faucet fully, and set the ball valve to a very small flow/stream).

Here’s the dripping faucet. I added a gated Y onto the frost free faucet to be able to control the flow. A single gated valve will work fine, but I use gated Ys for all kinds of stuff so I have them handy.


5. Re-connect the hose to the faucet and go home.

The “slug” of chlorine is now trapped inside of the hose that supplies the float and tank. As the hose slowly fills (from the steady drip of the faucet) the slug is gradually moved along the length of the hose, eventually winding its way through the float and into the tank. Along the way, it is killing everything in its path. The dead bugs and biofilm slough off and are flushed into the tank. Once the slug reaches the tank, the chlorine disperses, continuing to kill bugs until the chemical potential has been exhausted.

When you arrive back at the tank the next day, dump the tank and open the faucet. If the tank still smells strongly of chlorine, dump it again and re-fill. In all likelihood, your float will function perfectly and the tank will be sparkling clean.

The slug method is a very primitive technique for disinfecting lines, floats and tanks. It is also easy and effective. There are so many different types of water systems, I cannot possibly list the details that will work on your place. Still, the basics remain: mix some chlorine solution and find a way to introduce it into the pipeline, then allow the chlorine to slowly move through the system. Remember this: every existing faucet can provide a way to introduce chlorine solution to the system. The trick is to think about pressure and hydraulics. Find a way to move the chlorine slug in the direction you want it to go. Then, say goodbye to bio-film!

Happy Grazing!

*This message comes to you from the Slug Capital of the Universe: Western Oregon, where the unofficial State Mollusk is the giant banana slug.

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