Water Butt Overflowing
Dave Humby
Posts: 1,145
Folks, I recently purchased and installed a water butt with a feed from the garage downpipe. Now I took some time to read the instructions and even watched a YouTube video however somewhere along the line it looks like I must have my geometries wrong so I'm hoping one of you kind folks will help correct my schoolboy error!
Now the way I understood it the feed on the downpipe height should be lower than the top of the water butt. This way when the butt was full the feedpipe would backfill and therefore cascading the downpipe water over the reservoir and down the downpipe. Obviously the pipe from the downpipe to the butt needs a slight fall also for gravity to take effect.
All good so far, or so I thought! The butt overflows. So what have I c0cked-up? 
Posts
Once the water butt is full what makes the main flow change and go down the down pipe? Is there a valve of any sort?
Hi PP, there's no valve as such. The box section on the downpipe has a sloping internal 'channel' on all four sides which feed the outlet pipe. This channel I guess is 10mm by 10mm or so all the way round. As water runs down from the gutter on the inside edge of the downpipe it falls into this channel which then flows into the water butt. Now, the theory, if I understand it correctly is that when the butt is full the outlet pipe eventual fills up which in turn fills this channel up in the downpipe and therefore any more water that flows down from the gutter is in effect passed over the edge of this channel and down the downpipe to the soak away. That's the theory anyway!
Here's the piece of ket PP. Now that I've looked at this image I think the internal channel is maybe higher up the connector than I first thought. Maybe I just need to drop it slightly, whilst maintaining a 'fall' enough in the pipe that it will flow into the butt. Small margins between it working 'correctly' and not maybe?
Last edited: 20 June 2016 16:19:54
Yes that all makes perfect sense. So why isn't it working? It must be a height thing. Is your channel even a tiny bit higher than the top of the butt? It looks close in the picture. I looked at the one on Screwfix and the collar is quite high within the diverter.
HaHa that's the one I looked at! We crossed over.
I do not think that the hose leading from the diverter is high enough up on the downspout. Can you drop the water butt down to increase the gradient?
I would have gone the other way!
Try them both! Something's bound to work.
Then pp the water would not run into the butt.
Lowering the water butt would make the problem worse as the outlet pipe would not flood and therefore water would always be trying to enter the butt and therefore overflow.
PP you were right, it was a case of fine margins. I've just been out and dropped the downpipe a further 10mm or so down. There's hardly any 'fall' but there is just enough. I let some water out of the butt so it was 10mm or so below the top then poured some water in the gutter. I'm pleased to say this has done the trick and water could be seen coming out of the downpipe and the butt didn't overflow.
If I hadn't got the pic from the Screwfix website and noticed how hpith that internal collar was I think I would still be scratching my head now! Thanks to all for the input. Got there in the end.
Result!
Where the pipe comes out of the downpipe, this needs to be no higher than the top of the water butt. If it is higher then water will still flow into the butt. However, if its lower than the top of the water then it will be impossible for the butt to overflow. Water will fill the but only to the height of where the pipe comes out of the down pipe.
You can see from the line I've drawn on your photo that where the pipe originally came out of your down pipe, it was slightly higher than the top of your water butt.
Last edited: 20 June 2016 17:45:00