Drain them and put them into a large glass jar. I use half-gallon canning jars.
Bring the vinegar to a boil. You can do this over high heat if you wish.
Remove from heat and pour the hot vinegar over the raspberries. Make sure they are completely covered.
Put a non-metallic lid on the jar and sit it in a cool, dark, dry place. I use screw-on plastic lids now (you can find these in the canning section), but you can use plastic wrap and secure it to the jar with a rubber band.
You can continue to add fresh berries. Just make sure they are covered with the vinegar. You can add more hot vinegar if necessary.
After a month, I strain the liquid through cheesecloth. I squeeze as much liquid out of the raspberries the cheesecloth catches as I possibly can.
Discard – or compost – the raspberries you strain out of the vinegar.