Not really, storm water can enter through drain-waste-vents, gully traps and manhole covers. It can also enter when stormwater is accidentally connected to sewa

Not really, storm water can enter through drain-waste-vents, gully traps and manhole covers. It can also enter when stormwater is accidentally connected to sewage (it happens). You can seal off parts of a sewage system (eg. vacuum sewage between closed valves), but not all of it for practical and safety reasons.