Sumps, external pumps + drilling

[sphelps]

Depends on the pump really but all pumps will at least need an initial prime so it has some water to start, it will not start completely dry. Then depending on the pressure difference, the size of piping and the pump it may or may not be able to prime itself after a shut down. I would suggest a check valve which will keep the pump primed, it will only need to be re-primed if you remove the pump for maintenance.