# Applied: Containers without watertight cover of different height/size to be connected by a tube how do I fill them with water without overflowing?

I'm doing a bit of gardening and need help with a bit of physics. I've got 3 containers that I want to join and put water into. From which I'll fit a pump to draw water.

My goal is to maximize water volume and use all three containers, while reducing floor space (i.e stack at least one of them). The caveat is, their top lid is not watertight. They are 3 separate containers. I intend to drill and connect them with my 4mm hose.

*Edit: How about plan C? Will the below work, is there something on equilibrium that may help here by modifying the pipe. I'm scraping the end of the barrel here but there's this video online called the modified U tube, I wonder if it'd help in my set up?

If the tanks are open to atmosphere at their tops as you say, then the tops of the tanks will have to be level with each other. The water level will become the same across all 3 tanks if they are connected and not sealed at the top. If one tank is higher the water will drain into the others until they are all level. You should raise the shorter tanks until all 3 tops are level, then place the pump at the lowest point of the tanks as that is where the last of the water will drain to. The connecting tubes should all be at the bottoms of the tanks, once a tank's water level is below the connecting tube water will not flow to the others.

• Thanks @adrian for editing it on the gslide link. I realized the tube high up on the 27L in plan b was silly. Corrected it the screenshot. If I understand you correctly, the higher container will have more pressure. Why is this so, gravity force + atmospheric pressure? The top of tanks have a cover so it can stack on top of one another, but are not water tight, not over spilling will be ideal. Is there anyway to set it up so the "Ideal set up" which stacks the container on top of one another will work? (ie. If I placed the height of my tube at 159.- one cm lower than the bottom container) Dec 28, 2020 at 11:19
• (ie. Or can I apply pressure to the 4mm tube to allow only certain amount water pressure through, stopping after a certain height.) Dec 28, 2020 at 11:42
• To stack them the lower 2 will have to be sealed so the water from above does not leak out. Water pressure increases with depth. Dec 28, 2020 at 14:55
• Without resorting to sealing the water, could I use some form of equilibrium or modified U shape pipe to sort it out? I've edited the question a bit with what I have in mind. Dec 29, 2020 at 10:53
• @olif9837 Sorry for the lapse. A float valve in lower tanks is about the only way to control the gravity fed water supply from a higher reservoir when they are open to atmosphere at the top. see; en.wikipedia.org/wiki/Level_control_valve Jan 2, 2021 at 2:16

Per @adrian howard, this is the only way it can work now. I'm trying to find a way to minimise floor space it takes up without sealing the tubs.

You can stack the tanks if each of the lower tanks has a float activated valve (like in a toilet tank) which shuts off the input when the tank is nearly full.

• Nice, yea it sounds like this is what I need. Or at least is the right direction. Thank you @R.W Bird Dec 29, 2020 at 23:10