Minimize Clogged Drains - Plumbing Installation Tips

What is the correct size snake to use on a 1.5 inch shower/tub drain line? I get a recurring slow drain problem. After I snake the drain with my 1/2 inch hand cranked snake, the drain runs great for about 3-4 weeks and then starts to slow down again. I am told that my snake is not heavy enough to clear the drain properly.

Steven,
That is the correct size. The issue is the piping. If you want no clogs for years, you need to replace the tub drain branch line. I guarantee you that when you see what is in that pipe, you will wonder how anything ever got through.

I'm stumped. I moved the location of my kitchen sink approximately 10' from its original spot. I installed an air-admittance valve and am still having a problem with clogs. I snaked the line just to be sure that it's not something silly like a rag in the line. My new branch line is sloped, I have the AAV, dishwasher drain is looped (no airgap) the clogging happens too soon to be down the line in the old pipe. I think I'm getting some pretty serious siphonage. My AAV is 4" above the trap. The pipe going into the wall is pretty low in the cabinet, so there is about a 12" drop from the garbage disposal elbow straight into the trap. Any ideas out there? Please help, my wife is getting mad.....

We are building in Ellis County, Texas. Sewer/water lines were laid in yesterday but the kitchen sink & washer sewer goes across to the other side and joins the bathroom
sewer at 90 degrees. I can just see a log-jam at a corner like that.
Advice please. Thanks