T&T: re Holding Tank

[Peggie Hall]

> I've now come up with a
> problem on my nearly new, to me trawler. The holding tank hasn't been
> pumping out properly. 
> This came to light on a three day trip where the toilet seemly blocked but
> was actually indicating the holding tank was full....

Your tank vent is blocked. Everything you describe points to it:

> It appears (without
> digging into it) that the sediment may have solidified at about the halfway
> mark over some years and a small area around the pickup has been pumping the
> top surface out only. 

That's impossible.  There's no way that a pickup tube half full of 
sludge could pull ANYTHING out of a tank...'cuz the open end is at the 
bottom of the tube, at the bottom of the tank. So if there were a 
blockage ANYwhere in the pickup tube, nothing would get past it. Only if 
there's a hole in the pickup tube could anything be pulled out...the 
suction would lower the tank level to the hole and no further.

If your toilet was creating backpressure that felt like a clog, it's a 
sure sign that your holding tank vent is blocked...'cuz otherwise a full 
tank would be spilling out the vent, relieving the pressure instead of 
creating backpressure.

> ...when I run the pump out macerator pump it runs and then
> slows down to almost a stop like no voltage from the battery which isn't a
> problem, i.e. the load is too heavy.

Without a source of air to replace tank contents as they're being drawn 
out by a pumpout or macerator, the pump pulls a vacuum that prevents 
anything from being pulled out and does indeed increase the load on the 
macerator motor. A macerator motor isn't strong enough to pull hard 
enough to implode your tank, but a particularly strong pumpout can do it.

But holy COW!! some of the suggestions to solve this problem left me 
gasping!

> Disconnect it at the tank and blow (yeah I know, not too sanitary) hard to 
> see if you get a good puff out of the overboard fitting. If not clean it and 
> make sure that you have no low spots. Then blow into the tank (much less 
> sanitary) and make sure that fitting is not clogged.

The grand total of the federal bailout isn't enough money to pay me to 
put my mouth on a holding tank vent...plus it isn't necessary!

99% of  tank vent blockages occur in one of two places--the most common 
location is the vent thru-hull...critters love to build nests in 'em. If 
a tank is constantly overfilled so that sewage runs into the vent, the 
connection at the tank--both the fitting and that end of the vent hose 
is the only other place a blockage can occur...UNLESS there's a filter 
in the vent line or a sag in the vent line where waste can pool. Once a 
filter gets wet, the charcoal in it will swell and block the vent (one 
of the reasons I do not like filters). Both ends of the vent line can be 
scraped out with a screwdriver or similar blade--making blowing on it 
unnecessary...and if the filter is clogged, blowing through the line 
AIN'T gonna clear it. The only cure for a clogged filter is 
removal...the cure for a sag: shorten the line.

And btw, unless you want a VERY unpleasant bath, I wouldn't recommend 
removing a vent line from the tank before opening the pumpout fitting 
cap to relieve any pressure in the tank first. If the tank is seriously 
pressurized, there'll be an eruption, so I'd do that verrrrry carefully, 
with a hose at the ready.

> this talk about the horrors of holding tanks suggests to me something that
> Peggy Hall should invent - a holding tank polisher. 

It already exists, Ron...it's called a hose--not same one used to fill 
your water tanks, though. Although otoh that prob'ly wouldn't matter 
much to anyone who'd put his mouth on a tank vent. :)

As is true of every system on a boat, holding tanks--sanitation 
systems--require maintenance...so if you're looking for a way to avoid 
doing any, there isn't one.  It's also true of all systems including 
sanitation and holding tanks that PREVENTIVE maintenance is always 
cheaper and easier than cure...plus you get to do it on your terms 
instead of dealing with a crisis.

Holding tanks need to be thoroughly flushed out 2-3 times a year--and 
especially in preparation for winter lay up-to get rid of sludge...it's 
simple to do: after pumping out the tank, put enough water into the tank 
via the deck pumpout fitting--'cuz that sends the water into the tank at 
the bottom to stir up any sludge--to cover the bottom to a depth of 
4-5". Pump that out...repeat...repeat...till you're pumping out clean 
water. Or, keep the water flowing into the tank while running the 
macerator (btw, this can be done at sea using a washdown pump). 
Backflush the vent (unless there's a vent filter in the line) after 
EVERY pumpout and/or each time you wash the boat. If the vent thru-hull 
is a design that makes this impossible, replace the thru-hull with one 
that doesn't.

If the toilet uses sea water, the soft "crud" on the tank walls and 
pickup tube is mostly animal fats in waste. At least once a year--best 
time is in prep for winter lay up--pump out the tank and rinse it 
out...then fill the tank with clean water and a gallon of liquid 
detergent. Let it sit for a few days, then pump out and  also run that 
solution through the macerator...refill with clean water and pump/dump 
that out.

Any hard scale is usually sea water mineral deposits, only found in 
tanks that have sea water toilets. A 12% solution of muriatic acid in 
clean water will dissolve it. Follow all directions for handling and use 
of muriatic acid VERY carefully!

Finally, if your toilet uses sea water, a cupful or two of distilled 
white vinegar flushed once a week--not once a month or every couple of 
months or now and then, but once a week and ONLY distilled white 
vinegar, not cider or any other kind--will prevent sea water mineral 
buildup in the tank and the head discharge line.

-- 
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and 
Other Sources of Aggravation and Odor"
http://shop.sailboatowners.com/boat_odors/