Connecting tanks underground - will it work?

For our community garden, I'm exploring collecting rainwater for irrigation.  We have two buildings we can collect from.  One is inside the garden so we can put a huge tank next to it.  The other is 100' away and we'd need to get permission to add the gutters, a rain barrel and connect it to the big tank.  The connection pipe can't be above ground since they need to mow and we don't want a pipe in the way :(

I'm imagining putting a 55 gallon barrel at the distant building and connecting it underground with a 2" poly piping to the bigger tank in the garden.  When it starts to rain, hopefully the barrel will have enough capacity to have it's level raise, begin to move water down the pipe, and then equalize before it starts to overflow.  The distant barrel could be a couple feet higher in elevation than the big tank in the garden so that even if the main tank is 90% full, the little one will have the capacity to accept rain until the water starts moving down the pipe.  The distant building's roof is about 30x30 feet.  Our shed will be around 14x24 feet.

So....  Is a 100' long, 2" pipe big enough to do this job?  Are there other ways to get this job done?  Thanks!

That sounds like it will work.

Might be a good idea to put a cleanout in the middle, like a pvc riser with a threaded insert cap right at ground level. Then you could mow over it but still be able to get in there easily with a 50' pipe snake if you ever have to clean it out. For any pipes underground, the more cleanouts the better. All it takes is one winter of some bored squirrel deciding your pipe is a great place to store pinecones,

This will work and you probably don't need such large diameter tubing. If the remote barrel is that small, just figure out how quickly you'd like it to drain/equalise and size your line accordingly. I've got tanks and barrels interconnected with all sorts of sizes but the biggest is 32 mm and that is between the 800 and 1000 L tanks fed by the house and garage roofs. I like to use 25 mm tubing where it's also the way I get water out of the barrel array, just because it fills a bucket quickly. In the settings where I'm not in a hurry they're hooked up with 15 and 20 mm lines.

If it's really hosing down to the point where the little barrel is spilling faster than it can drain to the big tank, chances are your system is on the verge of being full anyway.

Thanks guys!  I guess the larger the tubing, the smaller the tank on the distant building can be.  

It's pretty common here for domestic rainwater systems to have the storage located some distance from the house and to run the line from the downpipe underground to the tank (wet connection). These are usually 80 mm PVC downpipe sections glued together, with a standpipe on the tank end and a cleanout somewhere accessible.

In the image, the standpipe inlet is the left one, and the one coming out the middle is overflow.

Thanks Phil!  Do you guys have to worry about the ground freezing at all?  I'm a little worried about having brittle pipes and/or joints underground for that reason.  Poly (if drained) should just flex around a bit without getting hurt if the ground freezes.  But it's limited to 2 diameter (I think).

Not in any of the populated parts of NZ, with the possible exception of the interior parts of Central Otago and Mackenzie country. Your system might need a drain and shutoff for winter.

Yup, I think there's a slight slope so we could drain the pipe and then divert the down spouts so it doesn't fill up at the first thaw...

Mike Haasl wrote:Thanks guys!  I guess the larger the tubing, the smaller the tank on the distant building can be.  

Yes, it will work. In an area with slow, steady rain you could use 1/2" without much trouble.

In area where thunderstorms deposit a huge amount of rain in minutes, and then move on, a bigger pipe may be better. Especially with a 55 gal. drum as the receiver. I guess you can do a cost analysis, though, on the cost of big pipe vs. a bigger storage unit like a 1000 litre/ 250USG cube.