What's the difference between a sewer manhole cover and a rainwater manhole cover?

The sign on the sewer manhole cover is "dirty", while the sign on the rainwater manhole cover is "rain".

Sewer manhole covers are mainly for sewage discharge, and rainwater manhole covers are mainly for rainwater discharge. Rainwater manhole covers, also known as rain grates, are generally made of cast iron, which requires high load-bearing. For example, there are many types of rain grates in Luwen, Hunan, so that rain grates of different sizes can adapt to different areas and facilitate the treatment of stagnant water.

Rainwater manhole covers are generally installed at intervals, and sewer manhole covers are installed on the road for a long period.