Our grey waste drain seems to block at the drop of a hat - I guess that basically it's undersized. We've resolved to do all our greasy washing up at site facilities in future - we have tried wiping off as much grease as possible before washing from frying pans etc. but to no avail. We have cleared the blockage before using a drain cleaner sachet (it's not completely blocked, just a trickle emerges) but having searched these forums I now realise one has to be careful what one uses to avoid damage. I've ordered a bottle of Fenwick's waste pipe and drain cleaner but I'm not sure this will be man enough to clear it. Any recommendations?