roof drain

• 浮顶油,罐的排水系统

roof drain的用法和样例：

例句

1. Leave the drain valve of the holding tank opened.
   让贮槽的排水阀打开。
2. At the bottom there is a drain hole edged with a brass eyelet.
   在底部有一个镶了黄铜小孔的排水孔。