My husband mixes Roundup in a small glass container and uses a small rag or brush (with rubber gloves on)to "TOUCH" each strand/blade of crab/quack grass. He likes to do this on very warm days and leaves it 2-3 days before cutting. You'll kind of notice that this grass always grows faster than the other grass around it so it's easy to single out.
Good luck

Not answering your question, but if it keeps coming up, you don't have crabgrass. Crabgrass is an annual that grows from seed each year. It does not run underground. If you pull it up, you would be pulling the entire plant. More likely you have quack grass, wild fescue, or a multitude of other grasses that run underground.

Round up is probably the best option. Since you probably have a very high root to topgrowth proportion, you'll need to apply multiple times. Leaves should be off color after aplication, but when they turn back to healthy green, that is your cue to re apply.

What will be happening is the poison will be absorbed and distributed throughout the roots, producing such a low concentration that it won't kill. You need to keep re applying until concentrations in the plant are high enough for death.

I had this exact same problem up until 2 weeks ago. I bought corn gluten, a pregerminate and haven't seen a trace of crabgrass since. I don't think that what the last poster suggested is true. Crabgrass creates so many seeds that when you pull it out you either shake off the seeds or stir the soil to bring up new grass. The corn gluten dries out the seeds (and any other seed you might plant) and leaves your garden crabgrass free. After 3-4 months it breaks down and seeds will germinate again. So if you're planing on growing anything new don't put corn gluten in that spot. Also, I've read that since it's also a fertilizer 10-0-0 to be carefull about the amount you use around flouring plants(too much nitrogen). However, it's perfect for herbs. I put it around my basil and dill and the nitrogen has really helped them puck up their growth. Let me know if you have any questions, but this stuff is awesome.

I guess I didn't explain clearly enough. What I meant is if it keeps coming up from the same roots, it is not crabgrass.

You are right, Khabibul, that crabgrass certainly can keep coming back from seed.

I have no crabgrass THIS year, after using a pre-emergent and doing manual weeding. But NEXT year how much will I have, from germination of LAST year's seeds?

Use round-up and you will not have to reapply--once is enough if it is quack grass that has underground roots. I use it every spring to kill quack grass that creeps into my flower beds and garden. Round-up kills what it lands on and is neutralized when it hits the ground so it won't kill seeds but it will kill the grass. It is slow to work but in 2 weeks the grass will be brown and dead including the roots.

I spray when it is not windy and will be sunny for a couple of days. I use a large piece of cardboard to protect plants I don't want to kill and spray close to the bottom of the plant I do want to kill. As soon as I dig out the dead grass I will plant and have never had damage to any plant in all the years I have been doing this, so I know it does not remain in the soil