If you have through-hulls for pickup you can take appropriately sized hose, stick it in the through hull
the other end to a barrel where you have a source of water. I am not sure about the exhaust
, you could just leave it open and let the water/exhaust flow out.
I have used a variant of this by using a bucket under my saildrive
with a water hose in the bucket. Not very elegant, but it worked for the relatively short time I was testing the alternators and charging