Saniflo and £2000 deposit

[Saniflo]

My friend recently moved into a new flat. It only had one a toilet - a saniflo one. After 5 days the saniflo toilet breaks and leaks sewage all over the place causing damage. The landlord's mate who is a plumber came over and said it was her fault as stuff was found down the toilet. She says the only thing she put down the toilet is toilet roll. Now she has moved out and they are now trying to get £2000 out of her deposit to pay for the damages. She maintains it wasn't her and must have been the old tenants as she only lived there for 5 days when this happened. Is she being unreasonable to dispute this and take it to the DPS (or whatever they are called) as she has no proof it wasn't her although she maintains it wasn't.

In all fairness, they have no proof it was her. If she was only there 5 days I think I'd refuse too

They are saying the damage actually cost £4000 and if she doesn't let them take £2000 now they will pursue her for the full amount.

Let them persue her then. There is zero chance they will prove this and I think it could be argued that having ONLY a macerating toilet isn't acceptable (it is against current building regs I think but that doesn't necessarily mean its not ok).

If it were me, I would be arguing that problems like this are part of the expected wear and tear where the only toilet is a macerating toilet. They are simply not designed to be used like that.