Holding Tank Swelling

7 posts / 0 new
Last post
x01203
Offline
Joined: 4/23/21
Posts: 3
Holding Tank Swelling

Greetings all.  So we just took ownership of a new-to-us 2003 36mkii.  While I have a few questions for which I may lean on this community, one that is most pressing is that of our holding tank swelling.

While we weren't present for launching, we were able to get out to the boat after a couple days for a shakedown.  Noticed almost immediately that the head became difficult to flush and got some backflow.  At first I thought maybe joker valve as there were no bubbles indicating a possible blocked vent.  

After a few more flushes throughout the day, I noticed the tank began to swell significantly.  I had initially ruled out a full tank as it has been pumped out for Winterization when hauled in the fall, and not used since.  Also, I would think if full, I'd see some waste coming up the vent line, but upon inspection at the elbow, it looked clear.  Is it possible it could be blocked at the stanchion?  Any easy way to check?  Not sure what the easiest access might be.

Another thought I had was that when the yard launched, they left all seacocks open...to include the macerator thru-hull.  I immediately exercised it and closed it.  Is it possible by sitting for a few days open the tank could fill with seawater?  It's been sitting idle on the mooring...no starboard tacks.  Also, I would think a filled tank would still push up through the stanchion.

I'll go ahead and pump out ASAP but curious about your thoughts?  I found a few similar threads on this but most seem to go back a few years.  Thanks in advance for any help you could provide!

Best Regards,

Kurt

 

Chachere's picture
Chachere
Offline
Joined: 10/27/10
Posts: 779

You may have figured it out:  The yard leaving all the seacocks open.   The holding tank is below the water line, so  leaving the macerator seacock open could very possibly permit water to syphon back into the tank and fill it.  We never leave that open unless operating the macerator (which we never do unless offshore).  For that matter, we never leave the boat in the water unattended with ANY seacocks open (not sure why a yard would launch that way....).

Matthew Chachère
s/v ¡Que Chévere! #466
1985 C36 MKI tall rig fin keel M25
Homeported in eastern Long Island, NY

Ken Krawford
Offline
Joined: 8/27/20
Posts: 5

Don't forget to check the holding tank vent.  A blockage would cause the same symptoms.  If it's blocked, you could experience a geyser when you open the pump out fitting !

x01203
Offline
Joined: 4/23/21
Posts: 3

So I pumped out, CAREFULLY opening the cap.  No geyser, thank god.  Disconnected the vent line from both ends.  Poured fresh water down the stanchion vent and it was clear.  Poured down the top of line and came out the other end.  Ran a wire though the elbow and no obstructions.  So....think I might have to attribute this to the yard launching with the macerator seacock open and the tank filling with seawater.  When I got on board I closed the seacock and used the head normally, not realizing it might be full.  Fingers crossed I might be on track now.  Thanks for all the help!

Chachere's picture
Chachere
Offline
Joined: 10/27/10
Posts: 779

Inspired by one of our other member's post - www.catalina36.org/forum/general-discussion/clear-pipe-head-hose-between-tank-and-macerator-final-resolution  -- I installed a short section of clear PVC pipe in the line running from the holding tank to the macerator; it takes the guesswork out of judging as to when the macerator has finished its job and the tank it empty (again, ONLY when offshore!).   Conversely, it made it apparent that leaving the macerator seacock open once the tank is emply permits seawater to start backfilling into the tank. 
So I do think you found the problem....
 

Matthew Chachère
s/v ¡Que Chévere! #466
1985 C36 MKI tall rig fin keel M25
Homeported in eastern Long Island, NY

x01203
Offline
Joined: 4/23/21
Posts: 3

That is a brilliant idea.  Thank you!

pkeyser's picture
pkeyser
Offline
Joined: 5/18/13
Posts: 508

By accident, we left our seacock open this year after launch and the holding tank filled. Because of the anti siphon valve, fortunately that's all that happened. Our C30 didn't have the anti siphon valve, and the same mistake resulted water/effluent pouring out of the head.
The C36 has another anti siphon valve located near the antifreeze overfill tank. It's a good idea to periodically unscrew the collar and remove/clean the rubber flapper so that it works properly. Most of us typically sail with the engine raw water seacock open. If the valve sticks the muffler can fill, and worse, seawater can enter the engine. 
 

Paul & Wendy Keyser
"First Light"
Newburyport MA/Rye NH
2005 C36 MKII #2257
Wing, M35B

Log in or register to post comments