Sewer smell - could it be linked to Sanispeed pump plumbing setup?

'Dirty brown bandage' looks suspiciously like Denso Tape, where someone has bodged a connection from the cast to plastic.
Probably - it has been like that for 45 years so I am not tempted to touch it! We will be doing some work in that room in the future so will deal with it then.
 
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