One Way Non Return Valve Strainers to attach to the top of pipes in tanks, aquariums and sumps to allow one way travel of liquid down the pipe, fitted at the end of line with flow activation.
PVC-U pipe and fittings are high quality, approved by the Water Regulations Advisory Scheme and fully reef safe. 
All pipe and fittings are metric and compatible with many other makes of metric pipe with joints connected using solvent weld glue.