Few things to check and the above post is one of them. The non-return valve is on the driver side, open the brake fluid cover, and its just under there. You can replace them with a connector pipe without the valve, it will work fine.
However, before you check this, check if you washer pump is still working. Does it makes a noise when you active them? Was it rear or front? Usually the pump is the issue rather than the fuse. You can get front pump for around £5-£10 but rear will be a tiny bit more expensive (£24 ish). Having said that, they are still cheaper than OEM at £40-£45 ish each.
Rear --> http://www.ebay.co.uk/itm/NISSAN-350Z-Water-Pump-Window-Cleaning-ADN10316-Rear-Blue-Print-28920-50Y10-New-/231742964107
Front --> http://www.ebay.co.uk/itm/FOR-NISSAN-350Z-2003-2015-FRONT-SINGLE-OUTLET-WINDSCREEN-WASHER-PUMP-/262462066955?hash=item3d1bf5510b:g:GCIAAOSwMHdXTZ7G
They are located just behind the front bumper, driver side. It is possible to get to the pumps without removing your wheel. Do a full lock to your left, remove few screw to bend the plastic lining and you will see the water reservoir and 2 pumps. I can't remember which is which. Press the tab to remove the connector (Rear and Front connector are slightly different to fail safe ie you can't plug in wrongly). Plug in new pump to test before removing old pump from reservoir. Once you tested and happy with it, you can replace them. They are not held in with any bolts or screws hence you can just pull it out but be ready with you thumb/finger to block to hole. Replace the pump and enjoy watching your washer working again