The house which built on pole base is sitting on a relatively lower site. Due to recently heavy and long term rainfalls. The basement (or you called it 'underfloor' as the height is not high enough for a man to stand up) is flooded. The rain/water is stranded underneath. Anyone knows what to do to improve the water flow on the ground underneath the house? Also, there is a green tank  in the ground (with a soft lid above the ground) at the front of the house in the garden. I believe this is to store the stormwater from the roof but I don't know what this thing exactly called, Is this to help the water flow for my house or for my neighbour which situated even lower than my site (to cache the stormwater)? If it's mainly for my neighbour, does it mean it belongs to my neighbour and they have the access right to it? Do I/or my neighbour need to maintain it regularly? It would be great if anyone can answer my questions. Thanks alot!