I do a few different things:
For the two boys in the huge cage, I fill the middle shelf up with hay(it's about 3 ft long, 2.5ft wide), this way they can eat it when they want to, or play in it -which they LOVE to do! They love running thru the hay, This way, most of it gets eaten, and they dont pee on that shelf. When I do happen to see poops there, I pick them up and get rid of them.
For the 3 boys in the smaller cage, I just toss in about 3 handfulls on their middle shelf, and spred it out. Let them play with it, and eat it- whatever they want to do. Most of the time , they play with it, and eat what falls down onto the bottom.
For the little girl in her own cage, she gets a hand full of hay that I usually spred over her tube, and she plays /eats in it.
I fill up all the hay when needed- usually ever 1-3 days depending on the cage.
I buy my hay by the 50lb bales(from oxbow , it's about 35 bucks only) and it usually lasts me a good 12 months for 2 chins and 4 pigs...but now i'm up to 6 chins and 5 pigs, so we'll see how often i'm buying hay.