You spend your day during chemo infusion time putting chemicals into your body. If you flush just once, it is possible that some of those chemicals may remain in the toilet bowl and splash on your family members, friends or visitors. Drink lots of fluids and be sure to flush several times.
And what about kissing? Well, as natural as a sweet kiss from your honey may seem, it is not a good idea to swap any spit for at least a week after chemo for the same reason as above. You need the chemicals given to you during infusion day but your family, friends, kids, and others do not need those chemicals in their system.
Isn't this just an "old wives tale"? Well, it may be but it is also true. Just use sensible caution as you go through chemo.