Actually there is no difference, V is not a strong sound but Turkish people are a little lazy lol so most of time when V is in the middle, it can be pronounced as "ğ" and the letter "ğ" is almost the same as "v" in "원". So you can actually pronounce "tuvalet" as "투왈레트". V is pronounced only as it is at the beggining or end of a word because it's impossible to pronounce it there. If you have noticed, there is no word starts with "ğ" in Turkish, and there is only a few word ends with "ğ" and it only makes the last vowel a little long

It's not like W but actually closer to English V. If you can say vast (U.K accent), vest, vodka, view correctly in English, i think you won't have much problem with Turkish v. It's a labial sound. Similar to p b and closest to f. Difference between p-b and v is. For p and b you make those sounds only with your lips. For b your vocal chords vibrate, for p they don't. You can touch and feel it. These sounds are kinda have a (ex)plosive feeling For V we also have teeth. This doesn't have any plosive properties. You make the sound by having the air pass (with friction) between your lip and upper teeth. For easier explanation.Try this. Stick your tongue out of your mouth (not too much just a little), and make F sound. Let your upper frontal teeth touch your tongue but do not bite or anything like that. Then slowly retract your tongue back to your mouth as you are continuesly repeating the F sound. Just as tongue is totally in your mouth you would definitely make a V sound. Edit: Do not put your tongue to your upper tooth's root. Retract it straight. But also you need to realize the sound :) Rest is up to you.

It's hard to tell. But you can listen the pronunciations of these words; 1. "Var" : https://tr.forvo.com/word/var/#tr 2. "tuValet" : https://tr.forvo.com/word/tuvalet/#tr 3. "sınaV" : https://tr.forvo.com/word/sınav/#tr