Clearing blockage via the manhole
The indicators of a blocked drain are poor flow, seepage of waste from around the manhole, or smells coming from it. To clear a blockage here, you will need a set of drain rods (available from hire shops).
If there is no indication of poor flow, smells may be due to an inadequate seal between the edge of the manhole cover and its frame. Inspect and repair as necessary.
Accessing the drains
Lift the manhole cover. This may be a two-man job as some covers are very heavy. There are usually two lifting points. These tend to get filled with dirt and debris and will need to be cleared. Depending on the type of cover, you may also need a cover lifting tool. This is a key type device which is inserted into the socket to enable the cover to be lifted.
When you lift the cover clear, you will see a pit through which the waste flows. One or more pipe runs may lead into it and one away from it.
If the manhole is full and you cannot see the outlet, you will need to judge at which end it is likely to be. This can usually be established by looking for other manholes and working out which one feeds which and therefore the direction of the outlet from the one you are dealing with.
Using drain rods
Assemble several lengths of drain rod. If the outlet is an interceptor trap (like a large- scale version of the trap under the sink, use the rubber plunger end to pump the blockage through the trap. If it is a straight outlet, use the screw claw end. Push this down into the outlet, turning clockwise only. Turning counterclockwise will unscrew the rods and you’ll then be faced with the task of their retrieval! When you feel it reach the obstruction, turn it gently and use it to push and pull. Be careful, as when the pipe clears, the retained waste water can be drawn away at quite a rate, pulling on the rod as it does so.
Remove the rods and flush the drain with water from a hose. Replace the manhole cover, making sure it sits flat in its frame.