Has anyone taken a drug test 4 days after using heroin and ped?hat would you like to ask?

My friend was using IV for about a week and a half, maybe 1/2 a gram a day. He has a drug test at his sub drs office and wants to be clean. Last use was Saturday afternoon and the test is Wednesday. Will he p? He's been drinking water, but not excessively. Or, if he does drink lots of water on Wednesday morning, will the test come back inconclusive?