AlphaUrd13
Junior Guinea Pig

if it helps, I use Kaytee glass bottles that are 175 ml and keep several of them depending how many piggies u got, since they tend to be sturdier and do the vacuum thing well in smaller sizes. At times if I twist the cap too tight the piggies don't get the water coming out so I close it without using extra strength and then tap on the ball thingie and if bubbles come out every two taps or so then it's a good pressure. Hope my method helps you handle the water bottle.