Qualex slurry bung.
Slurry spills can lead to hefty bills from the Environment Agency if they find their way into water courses, so having a spill mitigation programme is worthwhile.
The Telestopper, made by Environmental Innovations and sold by Qualex, is a heavy duty flexible bladder system to both prevent spillage and flooding.
Just insert the deflated bladder into the outlet pipe and pump up.
The system also works on corrugated and damaged pipes.
For a manual version, it costs £250.