No, if you install them correctly there should be no leaks whatsoever. There will be the occasional drip after a chicken takes a drink, kind of like a little dribble. But, they really are worth their weight in gold, that's why I created my byc page around them!! lol
Depends on your application. The heavier the plastic you use, go with the screw ins, the lighter go ahead and use the push ins with the rubber grommets. However, I have used the push ins with a 5 gallon Home Depot bucket, with no probs, just a bit of manuevering to get them in place. I actually sealed the inside of the bucket where the nipple was with food grade silicone. I was impatient and drilled the hole out just a smidgen too big and was not going to spend another 5.00 on a new bucket when I already had the silicone. Works great and did wonderfully for me all winter with a deicer! Sooooo much easier!!