I've had problems with my sink flowing slowly for some time now but on the weekend I noticed that the level of water in the toilet bowl was lower than normal too. That can be a sign of impending blockage so I thought I'd get a plumber in before it got that bad.
He put in a lot of effort but in the end he had to give up. There are two 90° bends where the waste pipe goes into the main waste stem and apparently something was lodged at least in the first bend, probably in the second bend too. I paid him £60 for his trouble but before he left, he gave me some advice.
So I trundled off to buy the product the plumber had recommended in the shop he had recommended. The name of the product was One Shot and it cost about £6. Apparently it's a very strong acid. The plughole unblockers you buy at HomeBase are all bases, i.e. have a high pH. Acids have a low pH. So this is the opposite approach. The plumber said that DIY shops aren't allowed to sell One Shot. I can only imagine what it does to the environment.
Anyway, I got home with the hallowed bottle and tried it. Following the directions and flushing with lots of hot water, the sink is now showing definite signs of improvement. I'm sold on this stuff.
The plumber's first guess about what was stuck in the bend was one of those plastic disinfectant baskets people hang in their toilet bowls. I've never used those, so if it is, it came from the previous tenant. That would make sense since I had problems with the sink more or less from the day I moved in.
It says on the bottle that you'll get the best effect in the morning. On the theory that the acid works better if the pipes are dry, I'm going to give it another go on Sunday afternoon when I get back from Cheltenham. I may still have an unblocked sink in time for moving out. That would be awesome.Update:
OneShot is only available from plumbing supply shops. Search yell.com
for "plumbing supplies" near your postcode.