in my health and safety course we were taught rats and mice are incontinent both with their dropping and urine and those can be found where ever they run also they leave behind greasy marks
Well, I think they need to change the food hygiene courses then, because that's actually not quite accurate
- they will leave behind grease marks if they repeatedly squeeze past/into something over a long period of time, but in general PurplePixie is right, they won't leave behind marks. They are not incontinent, they can control their bladders, but they DO choose to leave urine trails (scent marking) as they use that to follow to find their way to the same places again or to show ownership over something (male pet rats especially like to scent mark their owners - nice!). They tend to do their droppings in a particular area, a bit like rabbits - that's why pet rats can be litter trained, so you may not see the droppings at all if their toilet area is somewhere else.
PurplePixie is right also in that a male rat (and to be fair some female ones) would easily carry away an apple. The reason they probably didn't go for squash is because its a lot of effort to chew through the skin - why do that when there is much easier available food?! (though if you were kind enough to cook it for them they'd tuck in!) And onion is probably too strong for most rats - like purplepixie, mine never liked it. They like sweet things a lot - hence wanting apples.
PurplePixie, its good to see there is another rat lover on here - until about two years ago I owned them for over 10 years. Fantastic pets and very affectionate!
However, having said that, Mrs Ball, I recently had a 'plague' of mice in the house and totally understand how you feel about having them around - I scrubbed everything! (If that is indeed what they are!)