I don't believe CC can occur in a sewer. A sewer unit's only advance phase option is to emerge or not. Therefore it can't enter into another sewer location, so it can't enter CC in a sewer. Also entering a sewer from a manhole location is a MPh activity, so no unit can enter a sewer location in the APh. So no CC in a sewer.
The only way a demolition charge can be used in a sewer is if a unit in a manhole location throws it at a discovered sewer unit. The unit in the sewer would take a 30-2 and the thrower would take a 30+3+tem.
Did B8.44 change with the ASLRBv2? There are a few Adjacent manhole locations--remember >2 road hex-sides=manhole--and 1st. ed. B8.44 explains APh sewer possibilities. If you Advance into sewer CC, it's regular CC/Melee from that point.
8.44 APh/CCPh: Opposing units in the sewer system may not enter an enemy occupied Sewer Location during the MPh, and may end their respective MPh ADJACENT only if they are both beneath Manhole Locations in adjacent hexes. Should this situation occur, fire attacks between the ADJACENT units are allowed as normal during the DFPh and AFPh, and the APh can be used by the ATTACKER to move either to the Manhole Location above it (if allowed by the Sewer Emergence dr) or to enter into CC with the adjacent sewer unit(s). Since units in a sewer are always concealed (8.41) they are never locked in Melee, and during the next MPh the ATTACKER must move to a new Sewer Location.
Ok, so the ATTACKER (in the Sewer) can Advance into an adjacent Hex (in the Sewer) only to engage in Closecombat. Can the ATTACKER only advance if he rolls 4 or less (plus modifiers) since this is required to exit the sewer?