Thank you for the advice on the bag of solution and the angle of the needle. Fred doesn't have a lot of extra skin and he tenses up so it feels like the needle will go right into his body.
Fred's blood is bright red on the anus and feces, which would seem to indicate hemorrhoids or other lower system bleeding. But it had the distinct smell of bloody feces (I used to draw blood from patients at hospitals and nursing homes, and the smell is so distinct....).
Why is the k/d food bad for him? This is the only food available in my area for cats with kidney problems. What are the options for that? Fortunately he still has an appetite and manages to steal food from our plates when we are not looking or the kid's crumbs.
On the bright side, I heard Fred purr for the first time in a long time, and he is cuddling with me at night again after we started giving him Rubenal.