The central bank had to sell dollars on a net basis in June after an ealier spike in unsterilized excess liquidity and credit.
In order to collect reserves permanently the liquidity created from dollar purchases has to be mopped up.
Sri Lanka gets about 2.0 billion dollars of current receipts every month, of which about 1.5 billion US dollars are used in imports now. Some money is also used for outward travel and paying bonds.