A logic game on a grid where every square holds a pipe piece: an end, an elbow, a straight, a tee or a cross. Every piece starts at a random rotation and the network is broken. A click turns a piece a quarter turn clockwise. The first levels are small and the grid grows from there.
The level is done when no pipe end is left open and every piece is connected to the rest. The leaderboard takes the fewest turns, and time breaks a tie.
Three techniques solve a board without guessing. First, the edge decides for you. No end may point off the board, so an elbow in a corner has only one orientation, a straight along an edge must run along it, and a tee on an edge has one orientation too. A cross needs four neighbours and never sits on an edge. That alone fixes a good handful of squares.
Second, a known piece decides its neighbour. Once a piece is in place, each of its sides tells the neighbour whether a connection must be there or must not. That narrows the neighbour, which narrows the next one, and working inwards from the edges reaches the whole board.
The third technique is the loop rule. A finished network never contains a ring, so a connection that would join two pieces already connected to each other is wrong.