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Thread: Downpipe mod. into rainwater tank

  1. #1

    Default Downpipe mod. into rainwater tank


    I have a large 44 gallon plastic wine barrel that i want to use as a water tank (we have drought here in australia). I want to connect this to the down pipe that drains water off the roof of my apartment building. I had thought this would be a simple procedure of getting some fittings from a plumbing store but it's not working out that way.

    The down pipe measures 107.5mm on the outside diameter, which i think is actually meant to be 4 1/4 inch OD. This is my first problem as the standards are metric here and 100mm is all that people stock in terms of diameters of parts. So the only solution the guy at the store came up with i was getting a Boss Clamp called DWV PVC 100x50x87d (picture attached) and having this flow into the top of the wine barrel.

    The boss clamp (which i bought) looks like a t-junction that attaches to the side of my 4 1/4 inch pipe. I'll need to drill a 70mm hole in the pipe to allow for the t-junction to take some of the water into my wine barrel. I will then have a cap that i will screw onto the boss clamp when the wine barrel is full.

    So, my problems are that the boss clamp doesn't even fit the downpipe anyway so it will require a bit of heating to mold it to the larger size (as well as a lot of silicon). So there's the problem that i won't get a good seal and the large amount of water that can come down that pipe i a downpore could leak out.

    The other problem that i'm also worried about is that i won't get any water flowing through my t-junction. I'm on the first of seven floors and by the time the water gets to me it doesn't want to take a 90 degree turn to come into my wine barrel (i assume) so i'm worried all this construction won't get me any water. Perhaps i was thinking i'd need a little lip on the inside of the downpipe to direct water into the t-junction. What do you think? is this a really bad idea - creating a bit of obstruction in the down pipe to get some water into my t-junction? Perhaps this lip need to be removable so that when i'm not taking water into my wine barrel i don't still have that obstruction there.

    I've held off on constructing anything yet as i'm still thinking of returning the boss clamp as it's not a bolt on solution to my problem.

    Does anyone have any advise?

    thanks very much guys

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  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    I'd consider a rubber sleeve - one of those which SS hose clamps at either end. You might be able to stretch it to fit one end, and clamp it enough to seal at the other (depends on what's available which end might be bigger/smaller). What provisions do you have once the barrel is full? You certainly don't want it backing up in the downspout! Most of those I've seen have an overflow outlet. They are arranged so that you can daisy-chain multiple tanks together to expand your storage capacity.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3


    Thanks jadnashua,

    So do you mean to have a rubber sleave that goes from the end of that boss clamp pictured to my wine barrel (they do both have similar size entry/exits). Or is that rubber sleave meant for where the boss clamp connects to the down pipe, i can't really imagine how that would go on but maybe i just need to see a picture of the type of rubber sleave.

    As for when the tank is full, for ease of construction, i was just going to screw the cap back onto the boss clamp as you can see in that picture. I would like to have an over flow system but i'm pretty sure it wouldn't be water tight and i would have leaks which i really want to avoid.

    Do you think i would get enough water coming out that 90 degree turn? that's my main concern.

    thanks again


  4. #4
    Plumber patrick88's Avatar
    Join Date
    Sep 2007
    Webster Ma.


    Why cant you just get some rain leaders and reroute them to the drum. I would find it hard to believe they don't sell them someplace
    I'm just starting to work with an old friend of mine to bring solar electric and hot water systems, wind turbines, Flex Fuel Boilers, batteries, hydroponic gardening, books, pellet grills and more. Also the parts for DIY installation.

  5. #5


    I'm not sure what a rain leader is, i'm assuming that's a pipe that comes down from the gutter and feeds into something? something like this http://scrantonsewer.org/index_024.htm . I'm actually on the 1st floor of seven so having one of these come all the way down isn't a possability. there is that pipe which i want to connect to and do virtually the same thing.

  6. #6
    In the Trades Bob NH's Avatar
    Join Date
    Oct 2005
    New Hampshire


    One problem with tapping into the vertical pipe that comes down from the gutter is that you probably can't get any water out of it. They are often designed so the water drains out at the bottom without any significant water column standing in the pipe.

    If you can tap into a pipe that is nearly horizontal, or at least 30 degrees from the vertical, you can probably get water out the bottom of it. In that case your tap system would work if attached to the bottom of that non-vertical run.

    Tapping into the pipe at the bottom (necessary to get water) is also going to cause you to collect a lot of whatever runs off the roof. You barrel will end up collecting that sediment.

    If you are not the owner of the building or pipe you might find that the owner objects to your scheme.

    You will also have to find a means to stop the flow when the tank is full. If the tap is very much above the tank the pipe to your barrel is going to fill and pressurize the barrel if the barrel is closed. If the barrel has an overflow there is going be water running all over.

    There are a lot of details that depend on specific knowledge of the situation at the site. There are also a lot of things that could cause a big surprise if important hydraulic factors are not considered.

    The best way to collect runoff is to have the runoff pass through or bypass to the original dispersal point.

  7. #7
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
    Join Date
    Nov 2005
    Central Florida

    Default some thoughts

    First, as Bob NH advised, make sure the building owner has no objection to what you're doing. He may want some assurance that you'll restore his building to original condition if your schemes fail or otherwise are abandoned.

    Do you need the full 70mm-size pipe going into your barrel? You could try reducing the size of the output of your Boss Clamp to a diameter which would accomodate a slip coupling, and slip into this a piece of pipe with a tapered cut on the inside end, and a pipe or hose going to your barrel on the outside. Then you could slide the pipe in to the slip coupling as far as necessary to catch a useful amount of water.

    Is there a clamp similar to your T clamp that comes off at a 45 degree angle, rather than a 90? That might be a better way to divert the flow. There may also be a standard drain-system fitting like this designed to join a smaller pipe into the large down pipe at a 45. Just install this (permanently) (upside down, so the branch points downward) into the down pipe, and do the adjustable slip-coupled tap thing there.

    In either case, plan ahead to make it easy to restore the drain system to original, or close to it.

  8. #8


    thanks guys

    Unfortunately the only pipe coming down is a straight vertical one and if you think i'm not going to get any water out of it then i think i'll leave it as it is. I did want to divert the entire thing into my water tank and then have an overflow but i came into problems when no one was able to sell me something to attach to the non metric pipe. UNfortunately the only pipe the guy offered me was this t-junction, i'm sure there must be a 45 degree one but the guy didn't know about it. i think i may have to leave this project until i contact a plumber

    Thanks again



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