A container defined by where it gives up, not what it holds

A water butt, cut open in section. A downpipe enters at the top. Two-thirds of the way down, one hard horizontal line: the water. The overflow pipe leaves at exactly that height and runs off the right edge. Everything above the line is left empty — no water, no texture, nothing drawn in it.

That empty third at the top isn't unfinished. It's never going to hold anything.

What does this section actually show?

A butt at the only water level it's able to hold for any length of time — the height of its own overflow, standing next to the object it usually feeds: a can whose rose grades its holes to spread that water evenly once it's out again.

Rain arrives through the downpipe at whatever rate the weather sets. Once the level reaches the overflow, every drop above that height simply leaves again through the second pipe instead of piling up. The horizontal line in the drawing isn't a snapshot of one particular afternoon; it's the level the butt returns to every time it fills, which is why it's drawn hard and flat rather than wavy or approximate.

Why does the overflow sit exactly at the water line rather than lower down?

Because that's not a design choice being illustrated — it's the definition of where the water line is.

The overflow doesn't hold water back until some threshold is reached and then react; it's simply an opening in the tank wall, and the water can never rise past the height of an opening it can escape through. There's no valve, no float, nothing that has to detect the level and respond to it. The level is wherever the hole is, by the same plain logic that decides how far tea rises in a cup with a chip out of the rim.

What makes a good version of this design?

Leaving the space above the water line genuinely empty rather than filling it with a fading tint or a suggestion of splash.

The empty band is doing real work: it's telling the reader that capacity and volume aren't the same number for this object. A butt drawn brimming to the lid looks like it's showing you what the container is for; drawn two-thirds full with a hard line, it's showing you what the container actually does, which is different and more useful to know before buying one.

Who owns the shape of a water butt, or a marking like 32MM?

Nobody owns the shape. A cylindrical tank with an inlet near the top and an overflow set below it is a standard arrangement, built the same way by every manufacturer who makes one.

A specific brand's moulded tank, its printed logo and its own stated capacity belong to that company, licensable the ordinary way if a real one is the point of the shirt. 32MM here is an invented pipe-size marking rather than a real manufacturer's spec, which is exactly why it needs nobody's permission to print.

Does the same logic apply to any container besides a water butt?

Any vessel with an overflow set into its side works the same way — a bath, a sink, a fuel tank, a header tank feeding a system. None of them can hold more than the height of their own overflow, regardless of how tall their walls actually are.

Above ground, the same fixed-height thinking shows up without a pipe involved at all: cold air behaves the same way water does here, running downhill and settling at the lowest point it can reach, which is why a hedge across a slope creates its own frost pocket in the lowest corner of a plot on every cold, still night rather than only some of them.

Isn't an unfilled third of the tank just wasted capacity?

No, because that space was never available capacity to begin with — the tank's real size is set by the overflow's height, not by the height of its walls.

A taller butt with the overflow left at the same point wouldn't hold any more water; it would just have a bigger empty band above the line. The number that matters is where the second pipe sits, in the same way that the useful setting on a greenhouse vent arm is fixed by the wax cylinder inside it, not by how tall the arm looks. Buying by tank height alone tells you almost nothing about what it will actually hold.

Does it print well?

Yes — one hard horizontal line across a simple section is about as forgiving a shape as fabric gets, and the empty upper band means there's very little ink to lay down at all.

Cream on slate blue keeps the water line and the two pipes crisp against the ground; leave the water itself as a flat field rather than a gradient, since a soft fade at the surface would blur the one edge the whole design depends on being sharp.

How do I get one made?

Describe your section at JustOG — how full to draw the water, and what marking to put on the overflow. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.

Designs other people have published are in the shop.

A downpipe filling it, an overflow emptying it, and a line that never moves from between the two.