The Pool Manufacturer allows a player to score points when building houses that have a planned pool.
If a player writes the house number associated with the Pool Manufacturer effect in a house with a planned pool, then the pool is built. Cross off the top-most, lowest-numbered space in their pools column.
A player can use a house number/effect combination without a Pool Manufacturer effect to write a number in a house with a pool.
Oppositely, a player can write a number associated with the Pool Manufacturer effect in a house without a pool. However, in both cases, the pool is not built; therefore the player does not cross off a new pool in their pools column.