A rubber water reclaimer funnel (optional, but recommended)
Several lengths of hose
A large deep bucket (I used a kitchen garbage bin)
An immersion pump, with a float switch
A large storage vessel
A table (or similar support)
Step 1: Get the Water Out
Step 2: Grab a Shovel
Step 3: Drop in a Pump
The judicious placement of an ashtray into the bottom of the bucket (something that happened to be the right size and doesn't float) stops the pump from jumping around when it turns on. If it moves about in the bucket then it can jam the float against the wall, causing either your pump to run itself dry or your system to turn your garden into swampland.
Step 4: Attach a Short Hose
I bought a coupling for the 13mm polypipe from the hardware store where I got the pump. I had to hit the outlet elbow pipe from the pump with a hacksaw in order to get the coupling to fit. Not sure if that's what the manufacturer intended, but it seemed to be the only way this was going to fly.
I also resurrected an old table that was falling apart down near the back fence, and braced it in the hope of preventing it from crashing to the ground. All good so far.
I lashed the hose to the table with a small piece of wire, just to hold it in place.
Step 5: PVC Downpipe
Step 6: Polypipe
I ran 20m of 13mm polypipe around my garden plot. One end is rubber-glove-and-sticky-tape coupled to the system and the other has a plastic bung in the end, which I picked up from the store for about 50c.
Once I'd had a shower and had a nice full tub of reclaimed H2O feeding into the poly pipe (after quite a bit of testing and fiddling around to get it working reliably) I fashioned a tool from a sewing needle and a removable drill chuck for the purpose of creating sprinkler holes in the polypipe. This was deceptively good fun, as I discovered that I could spike the polypipe with the needle to create a mini fountain at whichever point, and in whichever direction and trajectory I liked. There was enough pressure from the water in the tub to shoot the water 30cm from the hose, if I got the angle right. So I spent a most enjoyable half an hour tiptoeing around bringing aqueous joy to every little patch of my garden, and revelling in the idea that I will be watering it every morning when I take a shower, with no worries about water restrictions.