DH and I are first time buyers and have been trying to buy a house literally all year (offer accepted in January, got to the point we were ready to exchange, only for everything to fall through). Found a second house in July which seemed perfect because it was a landlord selling up, so only us and them in the chain. Given how long this had been going on, we made our offer conditional on completion at the end of October. Needless to say, it's now mid November and the tenants have only just vacated 
On the advice of our conveyancers, we've been to look at the house this morning to confirm a) vacant possession and b) that the place hasn't been trashed since we last saw it. The idea was that if all was fine, we'd give notice to our landlord today, exchange next week and complete 1st December. All isn't fine: DH noticed that in the downstairs loo, we could hear running water. We lifted the lid off the toilet and noticed the cistern was empty. Taps work fine though.
We know nothing about plumbing and don't know if this is something minor like an issue with the toilet or something major like a huge leak. Our estate agent is contacting the vendors and asking them to get a plumber out and we are seeking our own advice independently also. However, our tenancy runs from the 15th to the 15th of each month: if we don't give our landlord notice today, we won't be able to for another month and will then be attempting to move over Christmas 
What would you do in this situation? (And does anyone know anything about plumbing?
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