Part of large undercover outdoor area with the pergola roof draining into the house guttering. The total roof harvest area exceeds the gutter’s capacity and prior to fitting a Gutter Pumper, the gutters regularly overflowed between the valley (at corner) and several metres to the RHS of the doors.  On one occasion, the house interior was flooded.




A vertical drop supplies 20mm horizontal pipe that primes the next vertical drop.





Note the 45 degree elbow used to reduce horizontal friction loss.
Not a drop has overflowed since installation.


To drain, a short 25mm poly pipe was fitted with a ¾” BSP X 25mm barbed poly director at one end and a 25mm barbed poly elbow at the other end. The poly elbow was then placed into a 32 mm hole drilled in the downpipe and a 20mm PVC faucet elbow was screwed to the director.  The 20 mm PVC faucet elbow then connected to the 20 mm PVC pipe and the gap between the poly elbow and the downpipe sealed.

If heated, a 25mm poly pipe will also tightly fit over a 20mm class 12 PVC pipe. A 25mm poly elbow is fitted to the poly pipe inside the downpipe. The flow of water should always be angled downwards inside the downpipe. A stainless steel ratchet clamp (not shown) will secure the poly pipe to the PVC pipe. Unless blocked, downpipes never contain less than two thirds air.

This Gutter Pumper is fitted approximately one metre to the right of a roof valley and flows into a grated drain at nearly 70 litres per minute. Pipes must remain either vertical or horizontal and the pipe’s diameter must not be increased prior to reaching ground level. Increasing or angling the pipes diameter will break the vacuum.












The minimum height of the immediate vertical drop is 65 mm as measured from the top of the baffle to the top of the horizontal pipe. The horizontal pipe plus the pipe length equivalent of 0.6 metres for each 90 degree elbow must be no longer than x 10 the initial vertical drop if a second vertical drop is to prime.

Example: A 200 mm initial drop must only service a 0.8 metre length of 20 mm horizontal pipe and two 90 degree elbows, a total pipe equivalent of 2 metres in order to prime the second drop.

A 20mm X 25mm  elbow increases pipe size to reduce friction loss over long ground level runs.




There was limited space to drill brackets to secure the pipe to the pole. The UV stabilised plastic tie not only sufficed, it was also cheaper and quicker to fit!




A hose end connector snap fits onto a sprinkler adaptor fitted into a 20mm PVC faucet elbow. The 19mm poly pipe diverts additional water to the garden.




Numerous houses have non compliant roof drainage
The downpipe near the garage (RHS) is 22 metres away from the downpipe (not visible) around the front left corner. There is a roof valley and four corners between both downpipes and evidence of damage from water flowing over the facia.
Fitting Gutter Pumpers to supplement downpipes during extreme rain events is clever  ‘insurance’.