>>It sounds like tilling is out of favor, and I'd rather not do it anyhow if I don't have to. I was thinking a load of topsoil would be nice to help level/smooth things out, fill in a few low spots and supplement the hard clay half of the yard.

In this instance, the soil is already disturbed from the tank installation. You can till if you want to.

And if you add top soil, you actually should till in this case to mix it into the existing soil. You don't want patches of this kind of soil and that kind of soil in the area, it'll lead to a patchy lawn with differing performance.

Plus thin layers of soil in dips and whatnot are asking for trouble. Roots dislike moving from one type of soil to another (although they'll do it if the layers are thin enough).

>>Not a big fan of the clumpy grass but is that common with all fescues or just poorly maintained lawns?

All fescues and ryes, but a well-planted and well-maintained lawn of these won't look clumpy. They do require reseeding more often as clumps don't spread.

Bluegrass doesn't clump and moves to fill in holes, but may not match the rest of your lawn depending on what it is.

>>should I be trying to time seeding for before or after rain? Or just adjust watering accordingly?

Just adjust watering accordingly. Trying to time seeding with rainfall is tough, and you're going to have to water twice a day anyway until the seed sprouts.

>>I will probably try and mail a dirt sample off to Logan Labs. Should I test the nice rich looking stuff, the crappy clay stuff, or a mix?

If it's part of the soil profile (and it is), a mix. I usually sample ten to twelve times across the lawn, mix it all together, and send it in.

>>while the other half has hard, dry brown clay.

More likely silt in New Jersey--but it doesn't matter. This is actually a great base soil to start with and, properly treated, will grow absolutely fantastic grass.