Macerator and Overboard Discharge Question

[and4ew]

I have holding tank that only has a deck fitting for pump out. It works fine but I'd like the option of pumping out the holding tank overboard where it's permitted to do so. Would I connect the output of the macerator to go to the same through hull as the head uses today (with a valve on the head side to avoid back up to the head)? Or should the macerator have its own discharge through-hull?

[nuku34]

I'm assuming you already have a Y valve that allows you to pump the head directly overboard via the through hull or to send the **** to the holding tank.

To pump the holding tank overboard, you will need to connect a separate hand operated diaphragm pump to the holding tank. You will need to install a hose fitting on or near the bottom of the tank and connect the input of the diaphragm pump to that via a hose. (Or you could put a Y valve in the pump out hose that goes to you deck fitting). The hand pump's output goes to a "T" installed between the output of the Y valve and the through hull fitting. Since the diaphragm pump is a one way device, you don't need a separate on/off valve to prevent **** going back into the holding tank when the head is flushing directly overboard.

[peghall]

Originally Posted by and4ew

I have holding tank that only has a deck fitting for pump out. It works fine but I'd like the option of pumping out the holding tank overboard where it's permitted to do so. Would I connect the output of the macerator to go to the same through hull as the head uses today (with a valve on the head side to avoid back up to the head)??

NOOOO...Absolutely not! Using the same "hole in the boat" for both incoming water for the toilet and and outgoing waste from the tank would be a disaster waiting to happen.

Whether you use an electric macerator pump or a manual diaphragm pump to empty the tank, you'll need a new thru-hull for the tank discharge. It CAN be above-waterline although not recommended because of the sight and odor from tank contents exiting the boat along with stains on the hull. It SHOULD be below-waterline with a seacock that should always remain closed except when actually dumping the tank. You'll also need to install a vented loop in the line from the pump to the thru-hull.

And you'll need a y-valve in the tank pumpout line--one side to the deck pumpout fitting, the other side to the overboard discharge pump. It should always be aimed for the deck fitting, switched to "overboard" only long enough to dump the tank.

If you plan to install this yourself, I strongly recommend you get some advice from your local yard manager who can have "eyes on" YOUR boat and can tell you exactly where to put the new thru-hull, mount the pump. etc. Any advice I could offer from here would generic.

---Peggie

[and4ew]

Hi,

I should have been more clear. I was asking about using the same hole as the head discharges today, not the intake. Maybe I should provide some back story. In Nova Scotia there are only a few places where you cannot discharge right from the head. Maybe that's not common elsewhere? There is both a raw water intake and a discharge. The discharge has a Y-valve that goes to a through-hull or goes to the holding tank.

My question is can I connect the output of the macerator to the discharge side of the head as shown? Perhaps with a second Y-valve (not shown) to prevent anything going up back towards the head.

The problem I'm trying to solve is that only way to empty the holding tank is to pay to get it emptied at a pump out station. These are rare in Nova Scotia.

[Bellinghamster]

Should be no problem to T into the toilet discharge after the Y valve. If the Y valve is in toilet->tank position it'll prevent the macerator flow from backing up into the toilet (s will the duckbill checkvalve on the toilet output, but they're not good for much backpressure, i.e. macerator switched on with discharge thru-hull valve closed ) Likewise, the macerator probably has a checkvalve on it's output that would keep effluent from backflowing through it to the tank when the toilet is flushed with the Y valve is set to toilet -> overboard. If a bit gets back into the tank it's probably not much of a problem.

[Windpilot]

I'd still put in a valve after the macerater. Don't rely on its checkvalve, either for the effluent but also seawater back flowing to fill the holding tank.

[jtsailjt]

Originally Posted by Windpilot

I'd still put in a valve after the macerater. Don't rely on its checkvalve, either for the effluent but also seawater back flowing to fill the holding tank.

If you T into your overboard line coming from your head prior to its vented loop that extra valve isn’t needed.

If your holding tank is in your bilge, chances are you won’t have access to anywhere near the bottom of it so much better to just T off of the pumpout hose with a Y valve so you can select either overboard discharge or pump out. Also, rather than a macerator pump or a manual diaphragm pump (I’ve had both for this purpose) a Whale Gulper electric diaphragm pump works well. By the time effluent makes it to your holding tank and sits awhile, there’s nothing left that needs to be chopped up. The slurry in your holding tank will pass through a diaphragm pump just fine. Since I always dump my holding tank while underway, I almost never notice just when the tank is empty and that means the pump spends some time runnng dry. That’s fine for a diaphragm pump but can be fatal for a macerater pump.

[and4ew]

Thanks all for the advice.