you can just unplug the sensor. its a plug at the bottom front of the washer bottle.
1. Black on Black 1999 LS400 PM-spec
-Maya-Megan-Magnaflow-LSportline-Xenondepot-Hankook-Duce-Platinum VIP-Figs Engineering-R1Concepts-
2. 1989 Toyota Supra white package
Current Status: -500 Internal System Error-
3. Black 2004 IS300 -Manaray-HKS-Eibach-
4. Ebony Teal 1995 LS400 11-8-06
The above will switch the light off but it will also disable a useful feature of the car.
The actual fix is not hard at all - To fix you need to remove the float switch which is accessible from under the washer bottle - it is held in place by a rubber gromet - to remove just wriggle it out and it will come out - you then need to dry it out on a heater ( i left mine on the heater for a week and afterwards gave it a coat of varnish to make it water proof before putting it back in)and then pop it back in again - thats it
The reason why the light come on is becuase the polystyrene float absorbs water over time and gets heavy and sinks tripping the switch and causing the washer fluid light to stay lit