I have two gigantic Salcuttas need a bigger pond and draining/cleaning is my focus. Seems the pipe, unscrewable cap, overturned bucket with rocks is common.Recommend a screen over the drain to catch the poop and sand to prevent drain hole filling over time? Am thinking 10' x 10' and 1.5' at the deepest. By the way, can tortoises walk/swim if their head goes under for a period of time?