It does look like you're going to have to use 45999 (Unlisted procedure, rectum). The coding depends on the depth of the intended examination and the specific tool used. Don't be tempted to use a CPT code that sounds similar to the service your physician performed.
Why not? For the anal canal, rectum, and the sigmoid colon (6 cm-25 cm), you'd normally choose a proctosigmoidoscopy code: 45303 (Proctosigmoidoscopy, rigid; with dilation [e.g., balloon, guide wire, bougie]). This covers the dilation, but specifically says the physician's using a rigid proctosigmoidoscope.
If the doctor examines the entire rectum, sigmoid colon, and perhaps as far as the splenic flexure (26 cm-60 cm), you'd normally use a sigmoidoscopy code: 45340 (Sigmoidoscopy, flexible; with dilation by balloon, 1 or more strictures). Your physician's using a flexible scope, but a Savory dilator isn't a balloon.
Bolster your claim: In your notes, refer to whichever of those two codes is most appropriate based on the depth of the examination as examples for purposes of reimbursement. You don't want to leave it up to the payer to figure out what a procedure is comparable to.