Basically, all of your carry over losses are "released" in the tax year you sell the rental property.
First, losses are deducted from any gain realized on the sale.
Next, if the losses get your taxable gain on the sale to $0 and there's a loss amount left over, the remaining amount is deducted from other ordinary income in the same tax year of the sale.
Then if that gets your taxable ordinary other income to zero and there's still some loss left over, it gets carried forward to the next tax year.
