The kitchen sink got blocked solid a few weeks ago, no idea why, water was just pouring down it and suddenly started backing up. Thought briefly about getting under the sink and unscrewing the u-bend as plan-b, but stuck with plan-a (plunger).
Just got out the plunger. Took about 5mins but the sink was eventually flowing again.
That plunger has unblocked the shower, unblocked the tub the washing machine pours into, and now unblocked the kitchen sink.
Many years ago I used to try and solve blocked pipes with that stuff they sell to pour down the plug holes to theoretically unblock them; which never made any improvement in water flow and they charge a lot for that stuff.
The plunger works 99% of the time. It cost less than $8. Everybody should buy one.
Doesn’t help with leaky taps though.