Am I required to have a perc test done before installing a septic system? Always 50% In most cases 25% Not sure 25% Get Free Quotes Today! Question: Am I required to have a perc test done before installing a septic system? Top Answer (50% of 4 votes): Always. Get Free Quotes Today! Find Local Pros Free Percolation Test Cost Estimates Related Questions How Much Does a Perc Test Cost? How long does it take to get the results of a perc test?Top answer: Less than 48 hours How Long Does a Perc Test Typically Take?Top answer: One full day (8 hours) What is a soil's percolation rate? Clay soils typically have slow percolation rates.Top answer: True