português para inglês Tecn./Engenharia Construção/engenharia civil Sewage treatment plant

I am working on the translatio of a websit of a Construction/Engineering company based in Portugal. There are many references to the Projects they have carried out incuding a description of the tasks involved in each one. I have come across the word "Exutor" numerous times, but don't feel that any of the definitions I have found so far are adequate:
"Execução do troço de Exutor por via marítima"
"Execução de Exutor submarine"
The terms I have come across such as "off-shore ewage outfall", or "drainage" just don't seem adequate.

Thoughts???