The screw-on caps are much less likely than the plug-on caps to fall off, so the straps are not really needed for them. If I did want to attach them (just so I didn't lose them while the hose was attached), the loop is much smaller than the one pictured, and can be attached to one of the screws.
After receiving additional information, it looks like this will solve my problem quite nicely, and probably last a lot longer than the rubber caps (and not get twisted). Thanks to all for your responses.
Gary Shapiro, 2011 Georgetown 29' Class A
Dash, Molly & Lily - now at the Bridge and forever in my heart
Shadow - 4-year-old Greyhound
Hannah - 1 1/2-year-old GSD rescue