Does anyone have any recommendations for making it easier to water lots of newly planted trees scattered around my land?

Our new place is on 25 acres of mostly open pasture, with a very few individual trees here and there. I'd like to get more trees established. I've already planted several around the house (but out of reasonable hose range) and I'd like to plant more, but I'm spending way too much time and effort watering what I already have.

I'm currently filling two 5-gallon buckets at the house, then carrying them to each tree to dump out. I'm giving each tree 10 gallons once per week during out hot dry summer months. With 9 new trees to water scattered around our house this is quite a job! Once my pond goes in I'd really like to plant a lot of trees around it. The problem is that the pond site is a lot farther from my house than the trees that are giving me fits now!

I'm currently looking at the plastic 100-200 gallon water tanks that fit in the bed of a pickup truck. They look perfect, but I'm wondering how much water pressure I'll get when I attach a hose to them. They work by gravity, with a hose attached to the bottom of the tank. I don't want to wait forever at each tree for enough water to drip out. Has anyone used these before? How fast does the water come out of the hose?

Any other suggestions for getting water to these trees more easily?