So, rather than thinking of it as two things at a time (singing while playing), doing 3 things (tapping, singing and playing) might be easier...
...well it works sometimes.
Epic post, as per usual! "Sometimes". Haha. If your instructions are followed, you will pretty much know how to sing whilst playing the drums too (which by the way is 5 things at once). Funnily enough i find it easier to drum while singing than play bass. Something to do with practise & habit i spose, i've been drumming for 17yrs but only bassing off and on for about 3yrs.
There u go folks. The human body can be fine tuned to perform & multi-task on so many levels!!!!