I'm working on a rainwater collection system.

Due to space limitations, I have arranged the barrels in a 2x2 configuration (as in the picture)

Problem with this configuration is that I can't get a good seal on the lids, and the 2 barrels on top never fill up.

Any ideas to improve the seal?

enter image description here

  • The barrels may seal better if they are upside-down. – Polypipe Wrangler May 27 '20 at 3:07
  • Sealed or not, stuff will grow in the water so it will only be useful in the garden without treating. – blacksmith37 Jun 14 '20 at 15:44
  • Plastic barrels of 55 gallon size are commonly used to ship chemicals . The ones I have came with 2 small threaded(?) openings, should be fairly easy to seal . I have since cut off the tops. – blacksmith37 Jun 14 '20 at 15:49

I would fill the top 2 first as a pair then the overflow from those fills the bottom pair, then excess can be dealt with.

Of course one issue, if there is to be only one outlet is how to connect the top and bottom without a manual changeover. That can be done with a oneway valve so the top ones don’t drain into the bottom ones.

enter image description here

Edit: to deal with air being sucked in consider a second oneway valve above the outlet as shown, once the upper tanks no longer have water then the valve will close.

enter image description here

Once the top pair are full the fill to lower tanks takes the excess until the lower tanks are full then the overflow bottom left controls the final level.

The outlet is fed from the top tanks until empty, then the oneway valve allows water out to the outlet from the lower tanks. If you don't have the oneway valve the top tanks will just empty into the lower tanks.

This has the advantage that the lids are now just dustcovers and are easy to remove / replace for cleaning.

  • Hi Mike, thanks for your suggestion. However I'm not sure I understand. The 4 barrels are connected and the outlet is at the bottom. The way I see it, no matter how I connect them the water will still escape.. – Juan Cortines May 26 '20 at 20:32
  • @JuanCortines see my edit, simple with a oneway valve. – Solar Mike May 26 '20 at 20:57
  • Brilliant. Thank you :) – Juan Cortines May 26 '20 at 21:15
  • you could also have a float valve (like in toilet tank) at bottom end of the red pipe ... extend the top end of the red pipe to the bottom of the top barrel ... the bottom fills by siphoning action from the top barrel when the top barrel becomes full – jsotola May 27 '20 at 3:23
  • 1
    @FreeMan, thanks for bringing this up :) This is something that I did not consider. My intended use is automatic lawn watering. One of the bottom barrels is connected to a water pump that will start automatically every day (or every second day). Because the total capacity of the system is not too big (120 L x 4, garden is also not big), I didn't even consider water stagnation issues.. yet – Juan Cortines May 27 '20 at 13:10

Ok, so I've drawn an alternate configuration based on the solution originally proposed by @jsotola. I don't know if it's the optimal solution, but I think it fixes a potential problem with lack of vacuum when connection a pump to the outlet. I apologise if does not directly answer the question, but I think it solves the main underlying problem. Either way I think it's worth to leave this answer here for posterity, although I will not mark it as the answer unless it gets upvoted by other users. Thanks! enter image description here

Update The float valve is still the best solution I've found so far. However float valves are quite slow, which cause two problems:

  1. While using the water, it's possible the lower barrels get empty while the upper ones still have water. This is not a big problem for me because I use the water every 1 or 2 days in small doses.
  2. While filling the barrels, it's possible the upper barrels get full while the lower ones are not full yet. Easy solution is to connect the upper barrel overflow directly to the lower barrel, adding a new overflow to the lower barrel.

Update I'm considering to replace the float valve with a float switch + actuated ball valve. The float valves I tried to far are painfully slow.


If reconfiguring the barrels, as suggested by others, isn't an option I would try two things:

1) Teflon Tape. In the past, I've used Teflon tape on a smaller diameter/volume container but similar working head pressure and it worked well. The lid must be fairly rigid or it would deflect around rather than compress the tape. As a result I had to use A LOT of tape. Likely one roll per barrel in your application. I eventually learned to replace the Teflon tape every time I opened the container and replace the lid every 10-12 times I opened it due to the plastic deforming.

2) Gluing. More permanent but more reliable. Obviously only for consideration if you don't want access to the interior ever again. I'm assuming these are standard polyethylene drums. PE is very hard to glue due to it's chemical properties, however there are some glues on the market which "activate" the surface to prepare it for bonding. Here is a brand available at my local hardware store.

  • Hi Andrew and thanks for the suggestion. I need to have the ability to clean them from time to time, so rather not gluing. I think I'll try the teflon tape if there is no better alternative.. – Juan Cortines May 26 '20 at 20:35

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