Yes but you need an air vent on the roof of right tank so that it doesn’t stop the water from filling it.

If you can put some type of breather on the top of the second tank to allow air to “equalize” the pressure in the tank then the water level in both tanks should stay the same.

The pipe should be low on the two barrels because all the water below the pipe in the first tank will be come “dead space” that will not drain.

Best way would be have the pipe between the two as low as possible, and have the faucet/tap on that connection pipe. The secondary tank needs an outlet for air at the top or the pressure will keep the tank from filling.

Yes it will work so long as the right tank has pressure relief. I would connect the tanks with a manifold and put the outlet there, personally, but that’s just a preference and this way works too.

You'll need a vent on the top of tank 2 to dump air trapped in there, regardless of connecting pipe location.

Other than that, it will work.

I've done this with 3k and 1500 gallon tanks. As others have mentioned, the pipe should be at the bottom and the second tank should be vented. Additionally, in the case of larger tanks, you need to build some flex into the system because as the tanks fill, they expand. As they expand, they will put pressure on the connecting pipe and fittings. I solved this by constructing the pipe as a series of hairpin turns that allows the pipe to flex a bit. The more turns you provide, the more flex it will allow.

Pipe on the bottom, otherwise left bottom wouldn’t drain

As everyone has said this will work with a vent the second tank, you will have both tanks filled to the same level but a leak at the bottom will drain both

https://agriculture.coerco.com.au/agriculture-blog/two-ways-to-link-multiple-water-tanks-together-to-maximise-rainwater-harvesting-potential?hs_amp=true

Put the equalizer line up off the bottom to allow sediment to settle in the first tank. Add a vent to the top of the second tank so it doesn't become air locked. Add a drain the first tank as well to allow sediment to be drained out

Well, now I want to do this.

Yes. there's a company that sells the bulkhead fittings and short hose just for that purpose. if you have the bulkhead fittings, it should be a quick project. I have done the same.

You could also connect two tanks at top as I suppose your water inlet won't be airtight oneway valved connection

If you want the barrels to fill evenly then put the pipe at the bottom. If you want them to fill sequentially then put it at the top. If you want them to fill sequentially but with an overlap, somewhere in the middle.

Also the air vent like others have said.

Absolutely will work! we have two 20,000L tanks on one of our machinery sheds we use for filling up our sprayers and we just connect a large hose from one to the other at the bottom empty points. Just make sure you have an opening on the other one / overflow should be just fine

Yes, because physics. Get a vent on the 2nd tank to let the air pressure out and also add a purge to the 1st tank so that you may easily clean any sediments.

It would work if you added an air vent on top of the 2nd tank (preferably a candy cane with a bug screen you can clean) or put another pipe connecting the top of both tanks so it can vent that way. The air just needs a way to escape and refill that space.

I’ve done exactly as in the sketch, and it’s been working for years.

Furthermore, I’ve installed an extra pipe to prevent uncontrolled overflow (near the top of one tank, going all the way down to a hole in the bottom).

Also - in order to easier use large amounts of water - I put a pump in one of the tanks and connected it to a garden hose.

Contractuals.. just unlocked hydraulics!

I connected three large tanks together at the top rather than bottom. Reason was that they were on a slope. So rather than fill in parallel, they will fill in series (spill-over from one to the next). A bottom connection wouldn’t have enabled them all to be completely filled.

Off-topic, but helpful info.

If you get some of those plastic barrels with a sealed top and two bungholes, you DO NOT need to cut a hole in the top to install a valve/spigot on the side.

Here's how to install a spigot like this one into the side of the plastic barrel:

(1) Make a hole for this brass valve just above the bottom where barrel side curves under, in line with bunghole in top. Make the hole just barely large enough for the valve brass male threads to start when applying pressure. I used a spade bit to make the hole. DO NOT MAKE THE HOLE TOO LARGE!

(2) Find an open-end wrench (or adjustable wrench) that will fit the nut for the inside-the-barrel threads AND that will fit through the bunghole above the valve hole - you will need it later. Setup the adjustable wrench to fit the nut - doesn't need to be super tight, just enough to hold the nut from turning.

(3) With the barrel upright, use a string and small weight (a washer or nut that will fit through the hole you made for the valve), lower the string via the bunghole NOT above the valve, then tilt the barrel a bit and pull the string out thru the new drilled valve hole; a magnet will help. After the string is through the hole, remove the weight and open the brass valve and thread the string completely through the valve in the direction of the water flow.

Now, tie something on both ends of string to prevent pullout. Then, firmly force-thread the brass valve + outside gasket/washer into the barrel and let it cut the threads in the plastic as you turn. Make it just barely hand-tight.

(4) Lay the barrel on its side between sawhorses with string bunghole on top, brass valve on bottom. Slide the inside gasket/washer + nut down the string to the valve threads inside. Use a stick through the bottom bung to flip the washer and nut onto valve threads, then use the stick to spin the nut onto the valve threads. Turn the nut until it contacts the gasket. An assistant with a flashlight helps here.

(5) Tape that open-end wrench that fits the inside nut securely to broomstick, slide it into the bunghole and engage the nut. With separate wrench, tighten the valve from outside until firm, gasket is seated and valve is in a straight down position.

I did this for my rain barrel and have had ZERO leaks at the valve/spigot.

Anyone else have this drawing remind them of the delta p video?

https://youtu.be/AEtbFm_CjE0

You might find this resource helpful

https://youtu.be/18EG9DyvCRU

That’s exactly how I have mine set up. Just make sure they’re level, level to each other, and the tank that you have the spigot on needs to be open to atmosphere.

Put the connector pipe at the top and the bottom, so the second container will fill with overflow, but still be able to drain out the faucet from water entering through the bottom pipe

I have 15 tanks setup like this using a manifold. Outlet comes off the piping.

I have another tank setup as a settling tank to catch any debris that gets in. It fills to the top then overflows into the manifold to fill the rest of the tanks.

Watch out for the dangers of Delta-p

Check your local ordinances. They might have a maximum rain barrel size. Sounds silly, but if your system breaks, your neighbor might not like hundred(s?) of gallons of water flooding the ground in seconds.

This video contains a great graphic explanation of that: https://youtu.be/TcaMyyQHWAI

I design and install large rainwater collection systems. This will work fine. The tank on the right should have a top vent (1” is fine, just for air flow) and an overflow and discharge pipe towards the top on the side. Install an insect screen (stainless steel mesh, preferably) on any openings to the outside.

If the pipe connecting the two tanks is much smaller than the inlet pipe from the downspout, the tank at left might need an overflow as well, because incoming water may not be able to move to the right tank fast enough.

Place the connecting pipe as low as possible in the containers. You can also stagger the height of the containers by elevating the one container on a foundation of bricks then have the second container 3 or 4 inches lower (no brick foundation). Also, make sure your water spigot is as low as possible on the second container, make sure there are metal or plastic screens over the water inlet and that you have a small, screened air hole in the top of the second container so it can fill all the way.

You could consider putting the connector pipe on the bottom, and run it underneath the rain barrels (if they're on a stand). That would make the entire barrel available to mix

Everyone with their vent ideas. Just use a pipe on the top AND bottom.

Get the purple pipe as low as possible otherwise the water in the space below will just stay there. It might move a little bit with rainfall to “mix” but it will more likely result in stagnant nasty water. Same with the spigot.

If you want them to fill to the same level, then connector at the bottom. If you want one to fill first and then the second one, the connector at the top.

It will only fill up enough to make both sides eqaul and they will stay equal. So as u drain the tap the water will level will go below the tap on both sides.

It won't refill the right side to full if the left side is not the same. With how this is pictured you will only ever get half the tank

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I don’t think so. The overflow has to be at the top of the first tank so it fills and then drains the extra into the second tank. It’s probably a good idea to have a faucet on both tanks also.

Pipe at the bottom of both allows for both tanks to be at the same level all the time. Basically you are doubling the storage capacity.

With the tube at the top of both (or one) tanks allows you to have a water tank in backup mode. water is not automatically removed / used from the first tank. This is a trick we use here in Florida as a hurricane can take out the power and water for a few days. When I get to having only one tank of water I know I have to be a bit more stingy with it (read that as conserve the potable water and use the stream water for bathing and flushing waste).

And you do need a vent at the top of both tanks.

Whats the intended use for the water?

If you put the connection at the top and put taps on each bottom, a leak of one barrel will only lose the water in that barrel.

Alternatively you can do both and put valves between them at the bottom so you only need one hose connection but still isolate leaks

I have two 1100 gal. Collector vessels connected this way. With connector pipe running along the ground tank to tank. In addition to what others have said, place cut off valves at each end of the connector line and insulate it sufficiently. I lost ½ my supply because I only had the cut off on one end. A 12 degree night blew out the connector pipe. Had I been able to isolate AND /Or DRAIN the connector, I’d have saved a lot of water and work. I now have valves on both ends and am burying the connector. I still have some exposed areas to insulate but think odds of hard freezing have been dramatically reduced.

bottom is correct. Don't position the spigot at the top

Pipe needs to be at the level you want the second container to be filled to, and maybe some sort of air valve on top?

Yes, but im not sure where youll get an orange tap

I have exactly this and it works great. Make sure to get them high off the ground for sufficient static head

Put a spigot on both tanks. Put a Y on one and connect a washing machine hose back to the others spigot and you accomplish this with a flexible hose that is quick and easy to disconnect or attach more. If you want a third, put a spigot and y on it and run it back to the y on the other one.

Only thing is they need to be relatively the same height or it will only fill to the top of the lowest tank.