Cost of Capital (WACC) -- Before- and After-Tax

Hey all, I am seeking some input regarding the WACCs/discount rates you use to find the NPV for before- and after-tax cash flows. I am looking at a NNN retail deal occupied by two tenants. Is it customary to go through the whole CAPM exercise, or is it more common to use a shortcut? Further, do you simply multiply the before-tax discount rate by (1-tax rate) to arrive at the after-tax discount rate? Really appreciate any insight as to how you determine your before- and after-tax discount rates. I have looked at a few text books and articles online, but seeing a lot of different things. Thanks!