Chambers could be full of crap, and still no smell should be getting into the house.
So whilst chambers should not be full, some standing water in the channel is not itself a problem, the problem causing smells is the waste pipework in the house, not the drains under it.
As mentioned smell does not enter passed u bends full of water , more likely you have a faulty durgo valve ( air admittance valve ) . Do you know where the top of your soil pipe is? External ? Internal? Which floor or floors do you have a toilet ?
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