Connecting a trench drain to a concrete manhole structure

December 14, 2017

Making the connection between a trench drain system and a concrete manhole can be a time consuming task if it was not planned properly.  Two types of connection are common.  The first is to stop the trench drain back from the structure and transition to a pipe.  The second is to bring the trench drain into the structure without any restrictions (note we call this connection type a "snout").  This second option when properly executed allows for  the trench drain to reach maximum flow capacity without restrictions. 

Before we talk about the hole in the structure we need to talk about the trench drain depth.  The precast concrete manhole typically will have a lid that ranges from 8" to 12" thick.  The trench drain system will need it's outlet connection to get under this lid.  If you want to use an 8" pipe and you have an 8" lid then the trench needs to be a minimum of 16" deep (and preferably a couple inches more) to come out the end.  If you do not have this depth the a pipe will require an elbow.  This is a place where debris can block the system and is typically avoided.  The other option is the snout.  A snout  will have a drop down in the trench t