This was a sewer line that kept getting clogged. We repiped and regraded it. The main line went to a house, while an additional one from an outbuilding joined the main line at the Y.
We also added a cleanout (upper lefthand corner) and used cast-iron piping. That is more expensive than clay or plastic, but is also more durable and long-lasting. Worth it in the case of something like a sewer line.