Misdesigned Holding Tank System?

[Bruce03]

Experienced ole salt getting a newbee experience on powerboats here...

The Wife had been complaining about "bathroom odors" whenever she flushed and my feeble attempts at humor got me The Stare .  I tried this and that but it wasn't until we hauled out and I was doing my best to winterize ... and then noticed the overboard discharge thru-hull hole was emitting brown water.  I opened up the hatches and got my mirror and long story short, my potty system was set up as follows...  head to macerator, to holding tank, hose from holding tank to stern, splitter, and left hose goes to pump-out opening on deck.  Right hose split goes to pump that handles overboard discharge. 

I've never used the overboard discharge so why was the brown stuff coming out?  Some research seems to indicate that the discharge pump itself should provide adequate "blocking" to prevent anything going through it unless it's pumping.  Well, something was going through!  Down below, I found a key that turned on the overboard discharge pump and it produced a considerable output, even though I had pumped the tank "empty" at the gas dock.

Here's my question:  Why is effeluence coming out via the discharge pump and what should I do to fix it?  I am planning to put a stop valve off the Y splitter, but could the pump need replacing?  It worked fine when we turned the key. 

I'm also surprised that the splitter is a plain old PVC from Home Depot.  Even more is that the hose, which is top of the line septic system marine hose is made from PVC.  I see "purple stains" on the PVC and I think that the hose is cemented into the Y Splitter just like ordinary PVC pipe.  It also has two clamps that I fear are merely decorations.  My view is that if the hose is PVC, then regular PVC cement is as good as any clamp(s). 

What's your take on all this?  2 cents worth and great thoughts welcome! 

[a7ewizard]

Sounds to me that the valve was in the "overboard" position when you attempted to pump the tank out. Was the tank so full that the head of pressure pushed fluids past the macerator's impeller? 

[Bruce03]

Sounds to me that the valve was in the "overboard" position when you attempted to pump the tank out. Was the tank so full that the head of pressure pushed fluids past the macerator's impeller? 

Well, there was no valve!  I've read that the macerator pump "normally" has something that blocks anything coming through unless the pump is on but someting was coming through.  The holding tank was just pumped the day before, although when I turned on the overboard discharge pump it pumped a quart or two out.  I can't find if this was the original design or if a previous owner went the cheapie route.  Is PVC used in our head system?  I plan to put in an on/off valve after the Y splitter on the hose going to the macerator.  Pretty simple, but hard to do because of the small working space.  I wonder why this wasn't done originally?   

What do the other Pro-Line boats have?

[a7ewizard]

Without a valve, wouldn't the dock side pump out just suck air through overboard discharge??

My 251 has a diverter valve (similiar to this: http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=15485&catalogId=10001&langId=-1&storeId=11151&storeNum=50632&subdeptNum=50646&classNum=50649).

It sounds to me that the prior owner micky moused the plumbing. You should be able to seach for marine plumbing diagrams to put your system back in operation.

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