Every time I go and use the rear wash on my Fabia I get a pool of water near the front passenger wheel, it only leaks when I use the rear not the front.

Open your bonnet, look at the firewall (bulkhead) on the passengers side, you should see a tube going through the bulkhead. The tube coming from the reservoir will have worked loose from the clip fitting on the bulkhead, just give it a firm push and it will clip back on again.

Does this help - Fabia-vrs.com - Repairs to Rear Washer Pipe - Fabia and Octavia (A4 / A5).