I'm North of Dallas, have a house on heavy clay soil. Foundation
watering is critical around here, not an option. I had a system put in
a few years ago, it's hooked up to the sprinklers so I can just set it
and forget it. I can share some things with you that might help..

I routed around the patio, but was advised to add a double loop there
so I did that. Only a few feet of extra hose. The driveway feeds a 2
car garage, we did the same things there. Bring the hose close, loop it
back so you have parallel hoses about 6" apart.

18" may be too far away, my literature search indicated 12" would be
better. Depth matters a lot, though - to get water around the edges of
the slab you have to get down far enough so the lawn won't steal the
moisture and so it doesn't have to take forever to percolate. I would
be concerned that a few inches depth might not do much in terms of
effectiveness. Remember that soaker hose volumes are small, and once
the hose is buried you get hydraulic lock VERY fast - the hose fills up
then the flow rate plunges as the water has no where to go. So you then
turn the water off, wait 15 minutes for it to settle, then you have to
hit it again. This still only puts down barely 1 ounce of water per
foot on average per cycle. I run my system on auto twice a day, every
day. In other words, if you are going to do this manually, you have to
be at the valve every day during the hot season for the watering to
make any difference.

The check for enough water is to drive a stake down about a foot and
pull it out. If the clinging soil is moist, your probably ok. Do this
at 3 or 4 points around the perimeter of the house.

Also, don't use a flat garden soaker hose, they don't work well when
buried. Get a real 1/2" diameter self-cleaning soaker hose. They're
cheap. Whoever you find that sells them will be able to get you an end
cap. You don't need a blow-off, just remember when you open the bib to
be slow about it. As for the end-of-hose to bib connection, you may
have to rig up something but that shouldn't be hard.

You can get Y-s with vavles on each side from a plumbing supply house.

Good luck,
Bill