Do you have size chart?

I do have a size chart and the exact waist size for a L on your site is the M size on the product

Does this clip to your bra? Also is there an opening for easy restroom use?

No this doesn’t clip to your bra and regardless of what the other posts say about this particular Spanx body shaper - this one DOES NOT have an opening to easily go to the bathroom - you have to pull it down every time you go to the bathroom!!! One of the main reasons I bought this item particularly was because the reviews I read and also in the “Questions” area I read that it does have the opening to go to the bathroom. Bummer!!! Besides that it is an “OK” body shaper!! It is a little thinner than other Spanx items that I have but just be a little careful pulling it up and down. Also it did tend to roll down which defeats the purpose of wearing one. I am 5’7” and weigh 145 lbs. & 36B. I normally wear a size 10 in jeans and a size medium in tops - I bought a large in this Spanx body shaper. Hope this was helpful.

Do these roll up your thighs after a few steps?

No, they are just a little bit thicker than pantyhose - mine never rolled- but they did snag 

What's a good detergent to use?

I'd avoid most of the standard detergents like Tide. They're not designed for the fabric that Spanx is made from and can actually clog up the fibers. I've had good results with Active detergent - it's made for materials like Spanx. Just make sure to get the one with the blue/white bag.