Line a sieve with a damp cheesecloth and place over a large bowl. Dump the yogurt into the sieve, cover with plastic wrap, and allow to drain in the refrigerator for 24 hours. Peel the cucumbers. Cut them in half lengthwise. Using a teaspoon, scrape out and discard the seeds. Grate the cucumbers into a colander, using the large holes on a four-sided grater. Salt the cucumbers and allow them to drain for 1/2 hour. Place the garlic, vinegar, and olive oil in a bowl and marinate while the cucumbers are draining. Squeeze the drained cucumbers as dry as possible and blot on paper towels. Place in the bowl with the marinated garlic. Add the drained yoghurt and stir. Add a few grindings of fresh pepper and salt if necessary. Serve with toasted pita bread triangles.