Gravity Holding Tank, Internal Tube or No ?

[SailingYoungs]

Hi folks,

I'm installing holding tanks on my Bavaria 49 as a requirement for sailing in the Puget Sound.

The tanks will be gravity drained, mounted above the waterline. There will be a 1 1/2 inch through hull mounted right below the tank for when I want to drain it into the sea. I also need to have the option to pump it out through a deck fitting.

So, I'm having the tanks custom made, and I have the option of having them put in a drain tube from the top or a hole in the bottom. If I put the pump drain hole in the bottom, right next to the other drain hole, the hose would then run from the bottom of the tank up to the deck fitting above the tank. Or I could have them put a hole in the top of the tank with a tube going to the bottom and the hose would have a short run from the top of the tank to the deck fitting above.

What are the things I should consider with making this decision, other than saving money on extra lengths of hose? Is the tube a better way to pump out?

Thanks!

Todd

[gonesail]

i have heard that the gravity system sometimes is not enough to avoid a stoppage in the drain hose. the dip tubes are a way to avoid risking a leak in a cracked bottom fitting on a plastic tank. you could always go with a manual or electric pumpout and have 2 dip tubes. your decision.

[swagman]

Have the top opening at the topof the tank, but with a tube welded in an ending close by the bottom of the tank.
Ensure you have both the lower drain hole and the bottom of the deck top tube in alignment.
That way if you ever do get a blockage in the bottom of the tank you can more easily push a rod down from the top to try and clear it.
If they are not aligned this would be impossible.
And you WILL get a blockage at some stage!
Cheers
JOHN