more tank space

[jrcinnh]

I boat on Lake Winnipesaukee, NH, no gray water can be discharged. The Searay answer to this, is to plumb all gray water to the shower sump and then have it pump into the Vacu-flush holding tank. Since that tank is only 27 gallons, it fills pretty fast if we use the shower.
I want to add another tank and there's room for a 25+ gallon tank.

I'm thinking that moving the gray water hose to the new tank would be pretty easy. How do I empty the new tank? I could add another deck pump out fitting. But is there a way to connect the tanks so everything comes out the existing pump-out fitting?

 

[fwebster]

You can make a manifold to connect the 2 holding tanks to a common discharge line and single pump out fitting. However, you must isolate each tank with a valve to so you only pump out one tank at a time. Without valves, once you empty the first tank, the second will stop pumping.

There is also the possibility of cross contamination and a huge odor problem as well as a health risk using a common gray water and black water pump out. I wouldn't do it this way, but if I did, I'd use a lockable "Y" valve so you have to make a conscious decision about which waste you were evacuating from the boat. It would be safer to use a second pump out fitting.

 

[jrcinnh]

I'm thinking valves have issues like remembering to switch them. But I also hate to put another hole in the boat. Let's say I put in another pumpout fitting, can I at least share the vent line. Can the cross contamination problem be any worse than it is now? Today everything goes in one tank.

 

[fwebster]

You need to look up a "Y" valve somewhere and see what it is. They are designed so that they are set to either one tank or the other but cannot be set to both. The more expensive ones have an extra position which is neither or "off".

As to Sea Rays idea in pumping the sump into the holding tank........this one sounds like a local dealers "fix" to me. Unless it is plumbed so that the discharge lines have a configuration like a "P" Trap in them, I have no clue why you are not getting holding tank odor in your drain lines. I just know that with a second tank you have the opportunity to remove the potential for a health and safety issue with fecal coliform bacteria in your sink drains. All it takes is a $25 deck plate and about a 2" hole saw.

If you are going to the trouble to install a tank and second pump out, why not install a new vent line as well. This one is about a $10 fitting and a 3/4" drill bit and 15' of 5/8" vent line. My problem here is odors and shortening the life of a very expensive holding tank filter, which you would not need on the gray water tank as long as you kept it clean.

 

[jrcinnh]

Believe it or not, it is a factory gray water system. I'm thinking that the sink drain odor is currently avoided because they all drain into the shower sump. Then the little bilge pump in there pumps all the grey water up through a backflow preventer into the top of vacuflush tank. The backflow preventer is probably keeping the odor out of the cabin. It probablty holds some water in the hose. There may be a trap between the sump and the tank, I didn't follow the hose behind the cabinets.

Thanks for the advice.

 

[fwebster]

Well, live and learn. We boat in a pretty big "lake" so none of the boats on the coast have a gray water system like that. It is legal to discharge everything but black water.