Technically yes, but if the hose cannot supply water fast enough I'd take the impeller out. Remember to start the engine first before pushing water through
No problem, just fit a couple of feet of hose into the existing hose and place other end in a bucket, fill the bucket and leave the hose running and it will be fine it won’t empty the bucket at idle speed. And I always just poke the hosepipe into the short extension to make sure the seawater pump primes under positive pressure, then when you see water exiting the exhaust you can just leave the hosepipe filling the bucket.