Use a piece of string and a level for the horizontal - once you have a level to work with you can adjust the depth required as you move down the garden.
this sounds like air in the system somewhere - bleed all radiators (www.diydoctor.org.uk/projects/bleedrads.htm) on the system - if its still cold after this - contact a plumber to test
You can buy a kit that caps of the waste outlet from Homebase or Focus - It's easy enough to do, but is it worth it? Depends - does your neighbour unblock the drain if its blocked or do you?
