Rainwater Harvesting for Drylands and Beyond by Brad Lancaster

How to Make a Flow Splitter with Inspection Hole and Natural Cork Plug

The following is adapted from, and meant as a supplement to, chapter 12 of Rainwater Harvesting for Drylands and Beyond, Volume 2, 2nd Edition…

I like inspection holes on the flow splitters in branched drain greywater systems, that way I can easily inspect them if they are not splitting the flow evenly, and easily clean out a clog should it occur. The following slides show you how to make and cap the hole.
Capping the hole will prevent soil or other debris from falling in, and clogging the pipe.

I use a natural cork to cover the hole to reduce my use of plastic and the fossil fuel consumption in its manufacture. This also makes it easier to make the hole in the flow splitter (less steps and fewer tools needed) and access it (just pull out the plug rather than having to twist it out) when compared to a flow splitter with a threaded hole and PVC plug.

What’s needed:
• flow splitter,
• 1 ¼-inch top diameter tapered natural cork (#14), available at most hardware stores (or make your own from a wine bottle cork)
• wax pencil
• uni-bit drill bit (this way you can make the hole to fit your cork). I like one with a ¾-inch to 1 3/8-inch range.
• drill

1 ½-inch diameter double ell flow splitter (made from black ABS plastic) and its label at plumbing supplier. You can show this photo to your plumbing supplier to order it.

2-inch diameter double ell flow splitter and its label at plumbing supplier.

Note that plumbing suppliers don’t call these “flow splitters.” That’s only a term used by greywater installers. “Double ell” or “double ¼ bend” are more common terms used by plumbing suppliers.

Place cork where you want the hole on top side of flow splitter.
Do not infringe on the flange into which the incoming pipe will be inserted; and do not go too far down the part’s split or crotch, otherwise water will flow out the hole.
Mark center where you want to drill the hole.


Center marked ready for drilling.


Drill slowly ensuring you don’t make the hole bigger than the cork, and don’t drill into the bottom of the flow splitter.


Hole drilled


Cork plug should only fit into hole enough to keep it firmly in place. Do not insert cork plug in so far that it could block flow of greywater in the pipe.


Making a flow splitter with a Y fitting – mark where you want to drill.

Hole drilled

Hole plugged with cork



For more, see chapter 12 of Rainwater Harvesting for Drylands and Beyond, Volume 2, 2nd Edition

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The Umbrella: Summer 2020

THE UMBRELLA: A catch-all of resources, events, media, and more from Brad Lancaster In this time of Covid-19 and spending more time at home to be safe, I’ve been grateful for the solace, inspiration, and bountiful sustenance my water-harvesting gardens, landscape, and neighborhood forest has provided me, my family, friends, and neighbors. Record summer heat […]

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