Does length of a hosepipe affect pressure/flow I have connected a hosepipe to my shower drainage plumbing (1st floor), which I am running into the garden (ground floor) as a kind of grey-water system. However, the water drains out the shower terribly slowly. 
The hosepipe is 50 meters long. I'm wondering whether the length is the problem. It probably only needs to be 20m to reach the end of the lawn. I don't want to cut it and ruin the hosepipe without knowing with some certainty that a shorter pipe will increase the flow/draining rate. 
Any opinions?
 A: Yes, you are correct that the length is the problem. As a matter of fact, in an application like yours the flow rate is pretty much inversely proportional to the length of the pipe: If you cut the pipe length in half, the flow rate will roughly double. The flow rate $Q$ in $\mbox{m}^3/\mbox{s}$ is given by
$$Q=\frac{\Delta P}{L} \frac{\pi D^4}{96\mu},$$
where $\Delta P$ is your pressure drop in Pascal ($\Delta P=\gamma\,h$, with $\gamma\approx9{,}810\,\mbox{N/m}^3$ the specific weight of the water, and $h$ the elevation of the inlet over the outlet), $L$ the length of the pipe, $D$ its inner diameter (all lengths are in $\mbox{m}$), and $\mu\approx8.9\times10^{-4}\,\mbox{Pa s}$ the dynamic viscosity of water. Notice that, if you could use a hose with a larger diameter, you could potentially gain a lot more than by shortening the pipe. Double the diameter of the pipe, and your flow rate increases by a factor of 16. That's assuming the flow stays laminar, which may or may not be the case; but you will increase your flow rate significantly even if you get turbulence.
