Single voice traversing multiple staves (piano score)

I'm writing a piano texture that has a melody that moves a lot between the upper bass clef and the lower treble clef, with lots of stuff going on above and below it. When it hops from one clef to another I need it to be understood that it's the same voice, rather than be treated as two intermittent voices in two different clefs (with all the extra unnecessary rests etc. that that entails). For instance, I know there's a way to take an upper-bass-clef A and shift it to the A below middle C in treble clef without having to create another voice for it but I've forgotten how, and all the keyword combinations I've tried lead me to an e-blizzard of too many entries to sift through. Thanks in advance for your help.