My kitchen sink has suddenly blocked. It was fine yesterday evening but then today when I put the washing machine on, water started to rise in the sink and took forever to drain. I've managed to take out the u-bend as well as the other bit of pipe and both are clear. Not sure what to do now........
I'd guess the block must be further down then. If the w/m water is coming up in the sink then it has to be after the pipes join. And since it was fine before today that suggests the pipe layout shoud be ok.
Try pouring down one of those pipe clearing products you can get. Failing that you may need to get something to poke down further. You can buy flexible tools to do this from DIY sheds.
Before pouring anything anywhere, you need to find where the trouble is. Have a look at the outside drain/gully and under any inspection covers. Only then should you decide further....