I have used caustic soda and other drain cleaners, have also checked manhole and still drain is blocked, can't see what with - it is the one from the kitchen sink and is used also by the dishwasher and shower.
You could try a length of flexible pipe (such as a hosepipe) with something harder securely stuck in the end (such as a piece of bamboo cane or old screwdriver)
Keep pushing this down the drain until it comes to a block then withdraw a foot or 2 and 'pound' the hose until the blockage gives way and the hosepipe moves freely.
Go to a plumbers merchants, and buy a couple of bottles of the proper stuff, smething like shift or one shot. You will probably only need one bottle(if that) but always handy to have.
Should cost around �5.00 a bottle.
It is serious acid, has ALWAYS done the job when other stuff has failed, and providing you are careful, is OK to use.
postdog is right. It's concentrated sulphuric acid and works like a dream.
But please be careful. Keep away from it. It gets very hot when in contact with water.
Just to add to your options; Use a pressure washer with a drain-cleaner attachment. This is a flexible small diameter hose with a wobbly metal bit on the business end which whizzes around under pressure,clearing all before it.
So first get your washer.........
If you don't already have a pressure washer, a far cheaper option is �20 for a set of manual drain rods.
Agree the acid should work though - it depends over what length the blockage has occurred (acid has to eat away from one end).
And you still have the drain rods for the next blockage. and if you really get into it, you could earn yourself a few bob unblocking the rest of the street.
I was clearing a blocked hopper when my dad helpfully put the pressure washer into the bottom end and turned it on. It cleared the blockage alright!! I was covered in gunk.
Caustic soda may do the trick but rods are probably going to be more effective if its a serious blockage. You could try a plunger as this may shift the blockage. Try and work out where the blockage is if you can or work back from the manhole - but this will depend on how far away the manhole is.
If you do use caustic soda, buy the proper stuff as Postdog says, not stuff from a supermarket. To be pedantic, caustic soda is actually alkaline not acid but equally harmful if you get it spilled on you.
Once you get it cleared, using caustic soda once a month or so will help to keep it clear.