I've Installed over 100 ponds, but have never used a bottom drain. I like the notion, but I am fearful of that seal leaking. Also, it seems that they would be better suited for a koi or liner pond. I like to build more the aquascape natural look with rocks & gravel. 1. What are your thoughts on them in general? 2. Do they accomplish anything with a gravel bottom? 3. Does the bulkhead fitting around the drain truly form an easy water tight seal?