First you need to diagnose the problem. I'm going to assume that the wipers are still working and the only faulty thing is that liquid is not coming out of the nozzles.
Get a friend to stand outside the car while you turn on the front then rear washer pumps and get them to listen for a noise (whirring of a motor). Of a noise can be heard then it is most likely a blocked nozzle or pipe. If there is no noise then the pump most likely needs replacing. Toyota parts can run you upwards of £45 so I went with one off eBay for £10. If I remember I will update with how it's held up after a month or so of usage.
As a precaution try sticking a needle down the nozzle and dislodging any debris before the next steps are taken as that does not require taking anything apart.
Getting to the pump to troubleshoot:
• jack up the front offside (drivers side) of the car and replace jack with an axle stand then take your wheel off
• there are a combination of clips and bolts holding the wheel arch liner in place. You only need to take the front and middle clips out, not the back ones as you are only folding this back. To take out the clips you need to get a screwdriver between the inner of the two rings and pop that partly out then pop the router ring out and the clip should come out. To get a bolt out just treat it like you would any other bolt.
• once the clips and bolts are out, fold back the liner behind the brake rotor and you should have access to the pump (only one pump which controls both front and rear nozzles)
• unplug the electrical plug at the top by simply pushing in the little button. Take the pipes off each side
• pry the pump out with a screw driver and be ready for the washer liquid to come out
• take out the black rubber seal and give it a good clean
• reverse this process being careful not to push the rubber seal into the reservoir and you have the option to put some electrical grease on the electrical connections
Clearing a blocked nozzle
• open the bonnet and put the stand up then use a screwdriver to pop out each of the black clips on the underside of the bonnet. They take a lot of force and unfortunately one of mine broke getting it out. I can not think of another way to do this
• take out the foam pad and pull the hoses off the nozzles. I found getting my fingernail behind the hose and pulling it back worked well
• use some pliers to compress the clips on the nozzle and then pop it out the top of the bonnet
• soak the nozzles in vinegar and give then a good swirl then let them soak for a few hours
• dry the nozzles and spray some pressurized air through them both ways with an air compressor or canned compressed air
• you can either put the system back together or and test or skip straight to next step but it involves getting to pump which is a more work
• get to pump like explained above then spray some pressurized air through the tubes when they are not connected to the nozzle and feel for the air coming out the other end
Assemble it all back together remembering to put the hoses and foam behind the hooks at the bottom of the bonnet and you should be sorted. Below is a video on further diagnostic and pictures I took along the way