• The drop manhole is a type of manhole in which a vertical pipe is provided.
• It is just provided just before the intersection of two sewer pipes. Sometimes it happens that the gradient difference between the two sewer pipe around 0.5m or more. So directly allowing sewage from branch sewer to main sewer will cause a big fall for the sewage.
• Drop man is also used in cases where providing a bigger sloping gradient to the branch sewer is to be avoided or is uneconomical in constriction.
• In cases where an inclined pipe is to be provided instead of a vertical pipe it is known as a ramp. The branch pipe is also extended up to the manhole and provided with a plug. This plug is removed whenever cleaning of the pipe is to be done with a rod.
• It’s an opening or hole constructed in a sewer for purpose of lowering a lamp inside it.
• It consists of stoneware or concrete pipe which is connected to sewer line through a T-junction. The pipe is covered with concrete to make it suitable.
• It is constructed when construction of manhole is difficult. In present practice use of lamp hole is avoided.
• This lamp hole can be used for flushing the sewer.
• If the top cover is perforated it will also help in ventilating sewer such lamp hole is known as fresh air inlet.