A very good newsgroup for this kind of stuff is uk.d-i-y - here is a simple Google search that has some articles - a tweak with the search terms should get it even better:

http://groups.google.com/groups?q=boiler+access+group%3Auk.d-i-y

Probably the single key recommendation people should take from this group is to NEVER buy a Saniflo shredding toilet system because they block at the slightest provacation. Everybody on the group who has owned one has been up to their elbows in sh!te trying to unblock it. My uncle has one and has also had to do this twice.

Gareth