The fan thing that you guys talk about is actualy a pump
and the fan things are blades to chop up sewage and rags.
The service hatch you talk about is the lid to the pump shaft to be able
to lift the pump out through the building, it's held down around the tube
at the top with forty 36mm bolts and is sealed with a gasket so it could not
be used as a way out. Please keep it in mind that these things are. Set to go off
automatically and when they do they pump out the sewage at a rate you wouldn't believe, that's what lifts the big flaps.
I know all this because I actually put them things in and remove them now and again for servicing. Be careful guys that's a very dodgy area.
Keep up the good work but play safe.