Provided always, that no occupier of any buildings or lands shall be liable to pay more money in respect of any expences charged by this or the special Act on the owner thereof than the amount of rent due from him for the premises in respect of which such expences are payable at the time of the demand made upon him, or which at any time after such demand, and notice not to pay the same to his landlord, have accrued and become payable by him, unless he neglect or refuse, upon application made to him for that purpose by the commissioners, truly to disclose the amount of his rent, and the name and address of the person to whom such rent is payable; but the burden of proof that the sum demanded of any such occupier is greater than the rent which was due by him at the time of such demand, or which has since accrued, shall lie upon such occupier: Provided further, that nothing herein contained shall be taken to affect any special contract made between any such owner or occupier respecting the payment of the expences of any such works as aforesaid.