Hi all.

I've got a question about harvesting our garage roof rain water.
Please excuse the long and rambling description.

Current situation is as follows...

Standard 1970s double garage (i.e. not big enough to get 2 modern cars
in ;-), flat felt roof, draining to the rear of the garage.

There are 3 rainwater hoppers. Right hand one goes directly into the
drain. Left hand one goes straight into a water butt (standard round
green jobbie). Middle hopper drops via a 22 degree joint into a 112
degree T piece into the left hand down pipe. From memory, it's about
2.8m between the left and right hopper centre points, and about 2.8m
tall (from the ground behind the garage). Looking at the back of the
garage, the neighbour's fence is to the left, our garden is to the
right.

ASCII art time

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Puddle Drain

This is all fine, with the exception that in heavy rain, the water
butt can be filled from empty to full in about 30 minutes. This means
that there's a very nasty swampy area, because all of the excess water
pours out of the butt onto the ground.

What we would *like* to do is replace the standard butt with a huge
1000 litre version, because watering the garden as it is, will take
~50% of the butt. (This isn't true, what we'd *really* like to do is
put a 40k litre underground storage tank in, with a floating pump,
divert all of the bath & sink water in, put in a UV filtration system,
and re-plumb the house to use this grey water to flush the toilets,
and have an automated plant watering system, but this seems a bit
pricey and over-complicated, so we're settling for a bigger water
butt!)

While we're replacing the butt, we'd like to sort out all of the other
plumbing.

Due to space and aesthetic reasons, the water butt *has* to stay where
the current one is (i.e. away from the drain). We ultimately want to
put a shed in the garden, and the garage wall is the only sensible
place for it, so putting a big water tank next to the drain would
limit the size/shape of shed, but putting it flat against the wall
wouldn't.

I can see 2 ways of fixing the plumbing...

1) Right hand hopper drops into the drain, with a 112 degree T piece
about halfway down. This goes up at 22 degrees where it goes into a
112 degree T piece (with a vertical rise) to the middle hopper, and
then carries on to the left hand hopper. This means that all the
rainwater will go into the drain. We would then fit one of those
standard rainwater downpipe capture collars, and take it all the way
back across the wall to the water tank with about 3m of the narrow
flexible hose.

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Drain

The main downside (as I can see) is that the wall will look like
something H R Geiger would be proud of. There's also a slight issue of
making sure that the narrow flexible hose from the collar to the tank
is exactly level, or it will never fill, or cause the tank to
overflow.

2) Drop all 3 hoppers straight down. Left hand via a 90 bend, middle
via a 90 T, into the right hand with a left facing 90, so it looks
like a W with a tail on the right hand drop.

We would then put a standard collar around the left hand drop, and
feed the tank as normal.

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Drain

The downside I see with this is that there is then no drop at all on
the lower horizontal pipe, which I just *know* will come back and bite
me if leaves etc get stuck.

I can't see any way (other than raising the tank on a 4 foot tall
pedestal), of using standard downpipe parts to put a decent drop on
the pipe *and* get the left pipe to the right pipe above ground, *and*
use a standard collar into the tank.

Does anyone have any ideas? Is it OK to have ~3m of horizontal
downpipe without a drop? Am I just worrying?

Could I even do something like a "K"? Keep the current arrangement of
the left and middle hoppers merging (so that I have maximum water
capture), then going off on another 22degree drop to the right pipe
and the drain, then putting a stop-end on the left hand down-pipe, and
attaching a smaller bore pipe, (or using an off-the-shelf adapter, if
you can get a 68mm to 12mm?) and then using a ball-cock valve in the
tank. This way you would always have a head of water above the tank,
but because of the valve, it at least wouldn't overflow.

My problem with this one is that in winter, if it froze from the top
down, it could crack the downpipe/valve

Thanks.

Pete.