Leaking Freshwater Drain tap

Evening All

I recently bought a 1999 Duetto and filled the freshwater tank for the first time today. There is a small leak on the drain tap and I wondered whether anyone could tell me how easy it would be to replace. Is there an internal nut holding the tap in place and what diameter the inlet pipe is?

Yes, internal nut, need to drop tank if you can't seal with silicon sealer.