Roger wrote:
The message
from "BRG" contains these words:

Nah! If the cover is not screwed down (and from your previous reply
it appears that way) then you can take some comfort in the fact that
there is no pressure there - if it was, then the lid would be on the
ceiling by now -
and I would suggest the blockage is *before* the manhole.

Just to muddy the waters a little shouldn't manhole covers inside a
house be screwed down as a matter of course?

Correct, but not all builders do that - or the odd D-I-Yer for that matter -
or they simply 'forget' to put the screws in :-)

BRG