I've not used the S much over winter and have found the washers getting weaker till this week they packed up completely. I assumed the one way valves to be fooked, but was wrong. The jets were blocked solid! Here's what I did.

1). First I pulled the pipes off at the elbow to the jet, gave it a squirt that confirmed the one way valves were fine.
2). unclipped the jets and removed them with the elbows attached, they came out really easily.
3). indoors I removed the elbows and gave them a soak in home brew steriliser/cleaner.
4). Attached a small length of pipe (about a foot) to the jets, tried to blow them through, no good so got a pin pushed it in the jets and gave it a good wiggle around, had to repeat this a few times
5). with the same sterilizing solution I ducked the jets in and sucked and blew the fluid through the jets, occasionally blowing some fresh water through from the jet end, loads of little black bits came out, presumably mould.
6). Kept at it for a while till it all ran clear and the water from the jets was strong and equal on both sides.

 

You can just leave the whole lot dismantled and soaking in hot water/vinegar for a while. Sucking through them is the sort of disgusting thing I'd do and isn't really recommended.

Same with prodding them with pins, really.

 

Compressed air from the jet end fixes it - or just throw them in one of those sonic cleaners. ALDI/LIDL do them from time to time.

 

A hair pulled from a wire brush with plyers and can do in situ, a good poke about may work also,

 

All good ideas, but not as much fun. And I know they are 100% clear now. Will repost in another 12 years.