Waster water tap

We have just acquired a 1996 Duetto.
The waste water tank has no tap and just a round hole where presumably the tap should fit  ?
Any ideas ???
Where to buy tap and how it fits to waste water tank.
Thanks x

I'm not familiar with your model  but do you need one of these?

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Hello (from near to you) and welcome to this most friendly and informative forum. The experts will soon answer your query but what little I know, the replacement tap will probably require access to the inside of your tank to fit the screw thread locking flange however there may be other options that may be less involved. Regards.