Sterilize jars and lids.
Place the cucumbers and tomatoes in a jar one by one, pour boiling water over them, leave for 10 minutes and drain the water.
Pour the measured amount of water into a small saucepan, add salt and sugar, and place on medium heat. As soon as the water boils, add vinegar and stir. Let it boil for another minute, then remove from heat.
Pour hot brine into the jar with tomatoes and cucumbers, screw on the lid and turn it over, cover with a warm towel.