Hello you lovely and kind folks!
So, here I am, getting used to busses and sends on most of my channels. I don't mind admitting to being a little overwhelmed trying to keep track of everything, especially after watching a zillion videos to do with mixing! Would anyone be able to offer a quick guess as to why I'm getting vocals coming through on my drum tracks? Each have their own buss and FX send/return. Apologies for being, quite possibly, a little stooopid!
 
Kindest,
Ainsley :)

Hi. Could you explain a little more? Is your vocal leaking to one or more individual drum tracks, or to your drum bus? How do you route your vocals and drums (including buses, sends, AUX tracks etc)? 
I think this might be a routing issue. We'll get to the bottom of it.
All the best.

Yes explain more - or even a screenshot.  

Is it possible that you're hearing vocals in your reverb bus? It is possible for some sends to end up in buses even though their source tracks aren't soloed - I can't explain the circumstances in which this happens because I'm not in front of my DAW, but if it's the case that you have your drums soloed and you're still hearing a little of the vocal, try muting the vocal track and see if that stops it.

I find patching more intuitive if I'm looking at the Console view, which is your mixer in Sonar.

Pre or Post fader button next to your send?
...sometimes I place a send in pre-fader, and that also ends up being pre-mute/solo as well.
So the sound still makes it to the bus the send was patched to...
Try post fader setting if in Pre fader.

Also - as someone mentioned, your patching...
Are all tracks going to the Master bus, and only one output from your IO is being utilized?
(shown at the bottom of each track in Console View.)

Sometimes I inadvertently change the output of a track to an actual IO output instead of the
master bus or other bus feeding the master bus.
That may cause both the master bus and track to play simultaneously, depending on how
your IO is configured.

I don't need to do it so much nowadays, but when I first started doing things with lots of sends and aux channels I sometimes found sitting down with a sheet of paper, a few pens in different colours and drawing the whole thing out as a signal flow diagram helped me keep track of what is routed to where.

I can't claim any credit for the idea, in the days of hardware everything and no computers when every session might need different things connecting up in different ways drawing routing and diagrams and keeping them with the session notes was how it was done.

Aww, you lovely folks! Many thanks. The problem appears to have been solved with correct routing of the vocal bus and "post" selected instead of "pre" on the sends. Doh! 
Your thoughtful replies were very helpful and much-appreciated.
Ains :)