Check on towerhobbies.com for the water pick up for the traxxas villains, then 5/32 aluminum tubing in 36" lengths, there are instructions on offshorelectrics.com on how to do all of this.

Then fill the tubbing with sand or salt and crimp both ends once it is filled, then wrap the tubing into a coil around something the same size as your motors.

then once you have your coils cut off the crimp on each end and figure out a way to get the salt out i found that rotating it and taping it at the same time worked best. What ever you do dont try to flush it out with water learned that the hard way.

And for a water exit you can do it really cheap by just cutting a hole in the hole that a water line will run throughand just have the line stick out of the hull.

Or you can buy a custom water exit at towerhobbies.

Hope This helps,
-Matt