You absolutly should be opening the window. Mrs Mercury refuses to shower without the darn thing jammed shut so if I'm about I'll sneak in afterwards and open it wide, it's a constant battle tbh, much like wiping down the walls around the shower after every shower which Mrs Mercury and the sprogs will not even contemplate doing.
Change fan for one that is Humidistat controlled.
Ensure hoses are clean internally.
Change outlet hose ro a rigid pipe sloping downwards (.025m per m run).
Put more insulation underneath the outlet hose or pipe.
Finally as per '76 - save water, shower with the wife!
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