Self-employed households and anyone with a big K-1 know the April problem. A number lands that's larger than any single month of income, and it has a hard deadline attached.
A line handles this well because the expense is one-time and the payback window is short. Draw what you owe, pay the IRS, then route surplus at the balance until it's clear. If it takes four months at $2,000 a month, you've paid interest on a shrinking balance the whole way down instead of a flat one.
Compare that honestly against the IRS installment plan. Their rate is the federal short-term rate plus 3%, plus a failure-to-pay penalty of a quarter percent a month while you're on the plan, plus a setup fee. Depending on where line rates sit, one is cheaper than the other, and it changes year to year. Run both.
Credit cards are the option to skip. The processor charges roughly 2% just to bring the payment in, and the card rate behind it is nowhere near a secured line.
Timing matters more than people think. The IRS charges interest and penalties from the original due date regardless of an extension to file, so an extension buys time on the paperwork and not on the money. If the line is going to carry the bill, draw it and pay by the April deadline rather than waiting.
The habit that keeps this from repeating: once the balance is clear, keep routing that same monthly amount into a set-aside for next year's bill. You already proved you could live without the money for four months. Most people who do this once end up funding the following April out of pocket.
Be careful about using the line for taxes two years running without fixing the estimated payments underneath. If the bill shows up every April and the line carries it every year, the line has turned into a term loan you keep renewing.