Lay pipe ahead of the flush. Every drain has to be fed, and nothing may spill.
The flow does not run on a clock — it runs on you. Every move you make pushes it one square further along every live branch.
So a split is a weapon and a debt: it reaches two drains at once, but from then on it eats two squares a turn instead of one.
Drag from a glowing pipe end to sketch a line — it turns where you turn, backs up to erase, and costs nothing until you let go. On release it sets in square by square, each one a move, the clock ticking underneath. A sketch that would end in disaster glows red before you commit. Draw out of your own plumbing to split it; hold an empty square to start a loose line. A dry pipe is never final: tap to spin it, hold to lift it and sketch a new shape in its place — both free. Undo takes back a whole line — even a losing one. When the network is sealed, it flushes itself.
White toilets push flow every 2 moves. Yellow ones, every single move. A sleeping toilet shows the moves until it wakes — and its plumbing had better be ready.
A numbered drain is backing up: feed it before the count hits zero. The parts bin is all the pipe you own — cast-iron mains are already in the ground, and you cannot touch them. Big boards pan — drag, two-finger scroll, or arrow keys — and pinch or the +/− buttons zoom.