Forgive me for making assumptions, but I presume that your attempts to clean your washer jets only for them to fail after a short time (so I presume they do actually deliver, albeit briefly) are down to a collection over time of scale, gunge and other associated particles accumulated over many years of use. If this is the case, then simply cleaning or fitting new jets won't help the situation as you will only drag more rubbish through to its narrowest point. What is needed is some careful deep cleaning of the reservoir, pump, non return valves and pipe lines.
Can I suggest that you detach the washer jets and attach two lengths of plastic screen piping over the original pipework in order to extend it (available at most good motor factors for reasonable money) long enough to divert the water flow into a bucket. Next, flush out the reservoir tank with a hose pipe and then re-fill using a strong detergent or a solution of warm water and bicarb of soda.
Next, run this mix through the washer system, allowing the solution to drain away through the extended pipes into the bucket, so as not to take the gloss off your paint work. When you have dispensed about 75% of the cleaning solution, stop the process and allow to stand for a couple of hours (leaving over-night is even better)
Replenish the washer reservoir with clean, warm water so that we still have a weak cleaning solution, and again, run this through the system. Finally, refill the reservoir and run fresh water through as many times as you need in order to flush out the system completely.
Replace your newly cleaned washer jets and all should be good. For good house-keeping, add some alcohol based screen-wash to keep it good.
Never use washing up liquid as it congeals over time and never top up from the Kettle as this way, you introduce limescale.
Hope this helps.. Kind Regards,
Eric