If you have loss under house property income and in other sources, should you tell to your employer so that lower tax on salary is deducted?

Yes, there is express provision u/s 192(2B) of the I T Act which states that such information should be given to employer in plain paper . The provision is given below
192(2B) Where an assessee who receives any income chargeable under the head Salaries has, in addition, any income chargeable under any other head of income (not being a loss under any such head other than the loss under the head Income from house property) for the same financial year, he may send to the person responsible for making the payment referred to in sub-section (1) the particulars of
•    (a) such other income and of any tax deducted thereon under any other provision of this Chapter;
•    (b) the loss, if any, under the head Income from house property,
In such form and verified in such manner as may be prescribed, and there upon the person responsible as aforesaid shall take
•    (i) such other income and tax, if any, deducted thereon; and
•    (ii) the loss, if any, under the head Income from house property,
also into account for the purposes of making the deduction under sub- section (1) :