This expression is used to refer to well-endowed bottoms, but its etymology is rather erudite. Exactly how this term came to be is a convoluted trip, so try to follow along as best you can...
In 1990, the Americans With Disabilities Act (ADA) was passed by Congress to better the lives of Americans living with a disability, particularly in areas such as housing and employment access. One of the things that came out of ADA was the wide-spread implementation of large lever-shaped door handles, which are easier to open than the traditional round doorknobs.
My ex-boyfriend Pucky (who's pretty ADA-compliant himself) used to refer to the dicks of bottomboys as "handles," as in "something to hold on to while you're having sex with them" He in turn got the term from his time in the porn industry (circa 1997-98), from a fellow performer who goes by the name Kristian Brooks.
Ira once famously left a post-P'n'M field trip fooding at the Posh Denny's in order to trick with a boy who calls himself "Oryon." We teased him about abandoning us, his friends, in order to get with this boy. Later, Ira described Oryon as having a large but oddly bent penis -- L-shaped, in fact. By this time (late 1998) I had been using "handle" to describe a bottomboy's penis and it had become common slang amongst the Magnificent Seven. Since Oryon was a bottom, and his "handle" was bent (like a lever), we joked that Oryon was ADA-compliant. Many other jokes were made at poor Oryon's expense, including "he can pee around corners" (Nutation), "he can stand sideways at the urinal and still get it in" (me), and "periscope up!" (Decay-).
Somewhere along the line, Nutation and I started using ADA-compliant to refer to any bottom with a big dick, bent or otherwise -- as in "easy to open up, with a big handle".