While this would allow you to discreetly slow-water the roots, I wonder about removing the hose/tubing when the tree doesn't need that much water anymore. If you are thinking of the same hosing that I am, the corrugations could make it hard to pull out. That said, it would be a way to provide several gallons of water directly to the roots, on a slow trickle, although you might have to devise some sort of cap to block the bottom end, so all the water doesn't run out there - on my clay soil, that wouldn't be a major problem - I have had a ceramic pot with a hole stay full of water for a day or more, sitting directly into the clay! The hose could stay in the ground, filled with mulch or gravel..., when the need for careful watering was done. OR, those hoses are large enough that you might be able to shred it from the inside with a utility knife, and remove it in pieces.

I have heard of people using capped lengths of PVC pipe - 4" or 6" diameter - in the same fashion, with holes drilled in them at 0.5-1.0" intervals. This would provide proportionately less water, but would be easier to remove when you are done with them.

I do think this might be overkill - a 5-gallon bucket, with several holes in it, would do much the same, with less effort. I grant, the aesthetics of a large bucket or two sitting at the base of a tree for an hour or longer, several times a week, might be lacking a certain refinement!

Of course with a proper mulch ring and just a couple of minutes with a hose, you're getting enough water to most trees, except perhaps those larger balled-and-burlapped or #20 to #25 or larger containers.

i have seen plastic pipe with holes.. installed vertically in a strawberry crock.. to insure water got further down the crock ...

but as noted.. i dont really understand why a tree would need such ...

on my slight slopes.. i have a moat on the uphill side of plants.. so that i can lay down 3 to 5 gals of water... which will stand there until it soaks in.. and i may return a couple times for a good soaking.. and not come back for a month in pure sand ... and then after 2 to 3 years.. they are free range ...

how old are these trees... how about some more specific facts about your problems... properly 'established' trees ... really should not be all that problematic... so how old are yours???

good luck
ken